I will begin at the beginning, and endeavour to repeat the entire conversation. On the previous days we had been in the habit of assembling early in the morning at the court in which the trial took place, and which is not far from the prison. There we used to wait talking with one another until the opening of the doors (for they were not opened very early); then we went in and generally passed the day with Socrates. On the last morning we assembled sooner than usual, having heard on the day before when we quitted the prison in the evening that the sacred ship had come from Delos, and so we arranged to meet very early at the accustomed place. On our arrival the jailer who answered the door, instead of admitting us, came out and told us to stay until he called us. 'For the Eleven,' he said, 'are now with Socrates; they are taking off his chains, and giving orders that he is to die to-day.' He soon returned and said that we might come in. On entering we found Socrates just released from chains, and Xanthippe, whom you know, sitting by him, and holding his child in her arms. When she saw us she uttered a cry and said, as women will: 'O Socrates, this is the last time that either you will converse with your friends, or they with you.' Socrates turned to Crito and said: 'Crito, let some one take her home.' Some of Crito's people accordingly led her away, crying out and beating herself. And when she was gone, Socrates, sitting up on the couch, bent and rubbed his leg, saying, as he was rubbing: How singular is the thing called pleasure, and how curiously related to pain, which might be thought to be the opposite of it; for they are never present to a man at the same instant, and yet he who pursues either is generally compelled to take the other; their bodies are two, but they are joined by a single head. And I cannot help thinking that if Aesop had remembered them, he would have made a fable about God trying to reconcile their strife, and how, when he could not, he fastened their heads together; and this is the reason why when one comes the other follows, as I know by my own experience now, when after the pain in my leg which was caused by the chain pleasure appears to succeed.Given Socrates disdain for the written word expressed in his "Phaedrus" (the myth of Thamus and Thueth, I am somewhat surprised at this "late" desire by Socrates to try his hand at poetry, especially as the author's ability to reminisce would be, in this case, extremely "limited".
Upon this Cebes said: I am glad, Socrates, that you have mentioned the name of Aesop. For it reminds me of a question which has been asked by many, and was asked of me only the day before yesterday by Evenus the poet—he will be sure to ask it again, and therefore if you would like me to have an answer ready for him, you may as well tell me what I should say to him:—he wanted to know why you, who never before wrote a line of poetry, now that you are in prison are turning Aesop's fables into verse, and also composing that hymn in honour of Apollo.
Tell him, Cebes, he replied, what is the truth—that I had no idea of rivalling him or his poems; to do so, as I knew, would be no easy task. But I wanted to see whether I could purge away a scruple which I felt about the meaning of certain dreams. In the course of my life I have often had intimations in dreams 'that I should compose music.' The same dream came to me sometimes in one form, and sometimes in another, but always saying the same or nearly the same words: 'Cultivate and make music,' said the dream. And hitherto I had imagined that this was only intended to exhort and encourage me in the study of philosophy, which has been the pursuit of my life, and is the noblest and best of music. The dream was bidding me do what I was already doing, in the same way that the competitor in a race is bidden by the spectators to run when he is already running. But I was not certain of this, for the dream might have meant music in the popular sense of the word, and being under sentence of death, and the festival giving me a respite, I thought that it would be safer for me to satisfy the scruple, and, in obedience to the dream, to compose a few verses before I departed. And first I made a hymn in honour of the god of the festival, and then considering that a poet, if he is really to be a poet, should not only put together words, but should invent stories, and that I have no invention, I took some fables of Aesop, which I had ready at hand and which I knew—they were the first I came upon—and turned them into verse. Tell this to Evenus, Cebes, and bid him be of good cheer; say that I would have him come after me if he be a wise man, and not tarry; and that to-day I am likely to be going, for the Athenians say that I must.
But also, IMO, the mystery solves itself "if" you conclude that it was his intention to satisfy himself that he had indeed been right all along to disdain the written account.