Do not follow a scribe who has been taken to prison, follow him after he has been taken to the tomb. (P. Onch. 8/9-10)While the general gist of the saying seems fairly certain, the exact idiom translated follow is unusual and is imperfectly understood. The idea is that while an intellectual (here a scribe) might have good things to say, those sayings can often get him in trouble. It is often not politically safe to follow someone who is in trouble and thus in the house of detention. Once he is dead, then he is no longer seen as a political problem.
The irony in this is that Onchsheshonqy is a scribe who is in prison. Perhaps Onchsheshonqy is simply warning his son not to follow in his footsteps until after he was dead.