Chayav inish l'vesumei, ad delo yadah
חייב איניש לבסומי, עד דלא ידע.
A man is required to drink, until he does not know
Gemara Megilla 7b says:
Raba said: A man is required to drink on Purim, until he does not know the difference between cursing Haman and blessing Mordechai