Fdb, thanks for providing the source.
Do you mean that غائب في الشراب (or is it الشرب?) does indeed mean "away drinking"? Is it, to your knowledge, a common/correct structure?
I do not have my books with me at the moment, but it rings a bell. It is in the story of the shoemaker and his unfaithful wife, sub-story in الأسد والثور. It is about how a wife meets up with her lover while her husband is away drinking with his friends. The story is missing in the censored editions.
PS. I have found it now in ʽAzzām’s edition of Kalīla wa Dimna:
وتخبره أن الإسكاف غائب فى الشرب وأنه لا يرجع إلا ممسيا وهو سكران