Martial, Epigrams 7.77
exigis ut nostros donem tibi, Tucca, libellos. non faciam: nam vis vendere, non legere.
You demand that I give you my little books, Tucca. I shan’t, as you want to sell them, not read them.
As often with ancient jokes, the punchline is weaker than we would like it today. I think we’d prefer ‘You don’t want to read them – you want to sell them!’