Exegetes of past generations assumed, I think, that this single pericope from the lost text involved two rich men, only the part about the second of the two (alter divitum), however, having been quoted in this excerpt. But more recently it has become more common to explain the "other" rich man as belonging to the second story of a sequence in the Diatessaron:
This idea seems very attractive at first glance. There are three stories in a row about rich men, and the wording of this story from the Gospel of the Hebrews presumes the sequence by calling this particular rich man "another" or "a second" rich man.
To my eye, however, it becomes less attractive at second glance:
|1||Arabic Diatessaron 28.33-41: 33 And a man of that multitude said unto our Lord, “Teacher, say to my brother 34 that he divide with me the inheritance.” Jesus said unto him, “Man, who is it that 35 appointed me over you as a judge and divider?” And he said unto his disciples, “Take heed within yourselves of all inordinate desire; for it is not in abundance of 36 possessions that life shall be.” And he gave them this parable, “The ground of a 37 rich man brought forth abundant produce, and he pondered within himself, and 38 said, ‘What shall I do, since I have no place to store my produce?’ And he said, ‘I will do this. I will pull down the buildings of my barns and build them, and make 39 them greater, and store there all my wheat and my goods. And I will say to my soul, “Soul, you have many goods laid by for many years; take your ease, eat, 40 drink, enjoy yourself.”’ God said unto him, ‘O you of little intelligence, this night shall your soul be taken from you; and this which you have prepared, whose shall it 41 be?’ So is he who lays up treasures for himself and is not rich in God.” (= Luke 12.13-21)||Liège Diatessaron 147, folio 49 recto, lines 13b-32, and verso, lines 1-7a, apud Daniel Plooij, pages 339-344: 339-344 Then one of the people came to Jesus and said thus, “Master, tell my brother to come and divide our inheritance with me.” And Jesus answered him back thus, “Man, who has made me judge and divider over you?” Then he spoke still further to the people, “Take heed and beware of all covetousness, for neither in the enjoyment of earthly riches nor in much possessing of transitory things is man’s life.” He confirmed this with a parable and said thus, “There was once upon a time a wealyour man whose grain had thriven well upon the field. And he said to himself in his meditations thus, ‘What can I do since I have not barns enough to store my grain in? This will I do. I will demolish my old barns and and will make larger ones, and therein will I gather all the grain that I have grown. And I will console myself thus, “Now you have many more goods than you could spend in many years. Now rest yourself and eat and drink and be at ease.”’ As he thought thus, there came a voice on God’s behalf which spoke to him and said thus, ‘Wretched fool, in this night your soul shall be parted from your body, and that which you have gathered, to whom shall it go?’ Thus it fares with him who hoards and lays up, and who is not rich in God.” (= Luke 12.13-21)|
|2||Arabic Diatessaron 28.42-29.11: 28.42 And while Jesus was going in the way, there came near to him a young man of the rulers, and he fell on his knees and asked him and said, “Good Teacher, what is 43 it that I must do that I may have eternal life?” Jesus said unto him, “Why do you call 44 me good, while there is none good but the one, even God? You know the commandments. 45 If you would enter into life, keep the commandments.” The young man said unto him, “Which of the commandments?” Jesus said unto him, 46 “You shall not commit adultery, you shall not steal, you shall not kill, you shall not bear false witness, you shall not do injury, honor your father 47 and your mother, and love your neighbor as yourself.” That young man said unto 48 him, “All these have I kept from my youth; what then is it that I lack?” And Jesus 49 looked intently at him and loved him, and said unto him, “If you would be perfect, what you lack is one thing: go away and sell everything that you have and give to the poor, and you shall have treasure in heaven; and take your 50 cross and follow me.” And that young man frowned at this word and went away 51 feeling sad, for he was very rich. And, when Jesus saw his sadness, he looked toward his disciples and said unto them, “How hard it is for those who have possessions to enter the kingdom of God! 29.1 Verily I say unto you, it is difficult for a rich man to enter the kingdom of 2 heaven. And I say unto you also that it is easier for a camel to enter the eye of 3 a needle than for a rich man to enter the kingdom of God.” And the disciples were wondering at these sayings. And Jesus answered and said unto them again, “My children, how hard it is for those who rely on their possessions to enter the 4 kingdom of God!” And those who were listening wondered more and said among 5 themselves, being agitated, “Who do you think can be saved?” And Jesus looked at them intently and said unto them, “With men this is not possible, but with God it is. 6 It is possible for God to do everything.” Simon Cephas said unto him, “Lo, we have left everything and followed you; what is it do you think that we 7 shall have?” Jesus said unto them, “Verily I say unto you, you who have followed me, in the new world, when the Son of Man shall sit on the throne of his glory, you also 8 shall sit on twelve thrones and shall judge the twelve tribes of Israel. Verily I say unto you, no man leaves houses, or brothers, or sisters, or father, or mother, or wife, or children, or kinsfolk, or lands because of the kingdom of God or for 9 my sake, and for the sake of my gospel, who shall not obtain many times as much in this 10 time and in the world to come inherit eternal life: and now in this time houses, and brothers, and sisters, and mothers, and children, and lands, with persecution; 11 and in the world to come everlasting life. Many who are first shall be last and who are last shall be first.” (= Matthew 19.16-26 = Mark 10.17-27 = Luke 18.18-27)||Liège Diatessaron 147, folio 49 verso, lines 7b-32, and folio 50 recto, lines 1-19a, apud Daniel Plooij, pages 344-353: 344-353 After that Jesus went out of the temple; and when he came upon the road, one came and fell before him on his knees and spoke thus, “Good master, what good works shall I work by which I may earn eternal life?” And Jesus answered him thus, “What do you ask me about good? No one is good but one alone, God. But, if you will come to eternal life, keep the commandments.” Then he asked, “What commandments?” And Jesus answered him thus, “You shall not commit manslaughter, you shall not commit adultery, you shall not steal, you shall not bear false witness, honor your father and your mother, and love your fellow Christian as yourself.” Then the youth answered him and spoke thus, “I have kept all these commandments from the days of my childhood. What do I lack yet?” Then Jesus looked upon him lovingly and said thus, “One thing you lack: if you wish to be perfect, go and sell that which you have and give it to the poor, and come and follow me: so shall you find a treasure in the kingdom of heaven.” When the youth heard that, he went away all grieved, for he was very rich and had many possessions. Then Jesus looked all round and spoke to his disciples thus, “How hard shall it be for those who have riches to come into the kingdom of heaven. And I say to you also that it is easier for a camel to creep through the hole of a needle than for a rich man to come into the kingdom of heaven.” When his disciples heard that, they were very much astonished and spoke thus, “Who then can be saved?” Then Jesus looked upon them and answered them back thus, “This is impossible for men; but all things are possible to God.” Then Peter spoke and said thus, “We have left all and have followed you. In what shall we be the better for it?” Then Jesus answered him, “Verily I say unto you that you who have followed me, in the resurrection, when the Son of man shall sit upon the throne of his power, you also shall sit upon twelve thrones and judge the twelve tribes of Israel. Verily I say unto you, whosoever leaves house or brother or sister or father or mother or wife or children or land for my sake and for the gospel, it shall be repaid to him here one hundred fold, and in the other world he shall possess eternal life.” (= Matthew 19.16-26 = Mark 10.17-27 = Luke 18.18-27)|
|3||Arabic Diatessaron 29.12-26: 12 And when the Pharisees heard all of this, because of their love for wealth they 13 scoffed at him. And Jesus knew what was in their hearts and said unto them, “You are those who justify yourselves before men while God knows your hearts; the thing that is lofty with men is base before God.” 14 And he began to say, “A certain man was rich and wore silk and purple and enjoyed 15 himself every day in splendor. And there was a poor man named Lazarus, and 16 he was cast down at the door of the rich man, afflicted with sores, and he longed to fill his belly with the crumbs that fell from the table of that rich man; yea, 17 even the dogs used to come and lick his sores. And it happened that that poor man died, and the angels conveyed him into the bosom of Abraham; and the 18 rich man also died, and was buried. And while he was being tormented in Hades, 19 he lifted up his eyes from afar and saw Abraham with Lazarus in his bosom. And he called with a loud voice, and said, ‘My father Abraham, have mercy upon me, and send Lazarus to wet the tip of his finger with water and moisten my tongue 20 for me; for, behold, I am burned in this flame.’ Abraham said unto him, ‘My son, remember that you received your good things in your life, and Lazarus his afflictions; 21 but now, behold, he is at rest here, and you are tormented. And in addition to all of this there is between us and you a great abyss placed so that those who would cross unto you from hence cannot, nor yet from thence do they cross unto 22 us.’ He said unto him, ‘Then I beseech you, my father, to send him to my father’s 23 house; for I have five brothers; let him go that they also not sin and come to 24 the abode of this torment.’ Abraham said unto him, ‘They have Moses and the 25 prophets; let them hear them.’ He said unto him, ‘Nay, my father Abraham, but 26 let a man from the dead go unto them and they will repent.’ Abraham said unto him, ‘If they listen neither to Moses nor to the prophets, neither if a man from the dead rose would they believe him.’” (= Luke 16.14-15, 19-31)||Liège Diatessaron 147, folio 50 recto, lines 19b-33, and verso, lines 1-31a, apud Daniel Plooij, pages 353-360: 353-360 When the scribes who were covetous heard this, they derided Jesus. And Jesus spoke to them and said thus, “You are those who make yourselves righteous before man; but God knows your hearts; for that which seems great to men is an indignity before God.” After that he confirmed this with a parable and said thus, “Once upon a time there was a man who was rich and clothed with purple and buckram, and who every day held great banquets. There was also a poor man who was called Lazarus, who lay in front of that rich man’s door all full of sores and longed to eat of the pieces that fell off the rich man’s table and no one gave him thereof. But the dogs came and licked his sores. Thereafter it happened that the poor man died, and the angels came and carried his soul into Abraham’s bosom. Afterwards the rich man died, and his soul was carried into hell. And when he was in torment he lifted up his eyes, and saw Abraham from afar and Lazarus sitting in his bosom. Then he called to Abraham and said thus, ‘Father Abraham, have pity upon me and send Lazarus here to me, and command him to wet the tip of his finger in water and to cool therewith my tongue; for I am sorely tormented in this flame.’ Then Abraham answered him thus, ‘Son, remember that you had your pleasant things in your life, and Lazarus poverty and unpleasant things. Therefore he is now in comfort and in pleasures, and you are in torment. And above all this, there is a great abyss between us and you, so that they who want to come hence to you cannot do that, neither can they who thence want to come hither to us accomplish that.’ ‘Then I pray you, father, that you send him into my father’s house, for I have there yet five brothers, that he warn them, lest they come into the place of this torment.’ Then Abraham answered him again, ‘They have Moses and the prophets; let them hear them.’ And he spoke yet further, ‘Nay, father Abraham, but if one comes who has been dead and speaks to them, they will do penance.’ And Abraham answered him thus, ‘If they hear not Moses and the prophets, they will not believe what someone may say to them who is arisen from death.’” (= Luke 16.14-15, 19-31)|
The fact is that, whereas there is a rich man in the second story, there is not really a rich man in the first or in the third; rather, in those stories, the rich man is part of a parable being told. Those rich men, the first and the third, are not part of the narrative of the gospel; they are part of stories within that narrative. And it does not seem very natural to me to narrate Jesus telling a parable about a rich man and then to say that "another rich man" has approached him.
I have considered that perhaps the "first" rich man was not supposed to be the fellow in the parable, but rather the man asking Jesus for help getting a share of the inheritance. But that man is not characterized as rich; to the contrary, he may well be desperate for a share of the inheritance precisely because without it he is poor.
Is it possible that the author or editor of the Gospel of the Hebrews either (A) treated the rich man with whom Jesus actually speaks in the narrative as "another" one after the rich man about whom Jesus speaks in a parable or (B) assumed that the man in the first story was already rich and wanting only to get richer? Sure. Not both at the same time, but either of these options on its own seems possible. What neither seems to be to me is self evident.
Incidentally, both Klijn and Luomanen write of three stories in a row about rich men, but the very next story in the Liège Diatessaron is also about a rich man:
And the next pericope, in both Diatessaronic texts this time, is a parable about how the owner of a vineyard pays his workers. Even the discussion which follows thereafter in both texts presumes a situation of wealth, with advice to invite "the poor" (and other disenfranchised folks) to one's banquet.
Various gospel authors and editors seem to have liked to group stories together according to shared features (witness the "controversy stories" in Mark 2.1-3.6, for example), and to group stories about wealth together seems unsurprising. With such sequence building going on around the topic of wealth, for "another" rich man in a truncated pericope to happen to fall somewhere in position 2+ of a sequence of stories about riches in one of those texts may not be a huge coincidence.
To be clear, Klijn lists many other possible points of contact between the Gospel of the Hebrews and the Diatessaron and its (mainly Syriac and Latin) allies, and each of those points ought to stand or fall on its own merits. My observation here is that the man in this pericope being "another" rich man may not actually be one of them.