Likutei Halachot: Ad d’lo Yada II

A person is obligated to drink on Purim until he no longer knows the difference between “cursed Haman” and “blessed Mordechai.” (Megilla 7b)

Therefore, one is obligated to drink on Purim until he no longer knows the difference between “cursed Haman” and “blessed Mordechai.” For there he is above knowledge, and there it is inappropriate to say, “cursed Haman,” for there it is entirely good, above the middot, above days of good and days of evil, as stated above. This is the aspect of the secret of the red heifer, which is the aspect of statute (chuka), above knowledge: it defiles the ritually pure and purifies the ritually impure. This secret will remain incomprehensible until the future when the hidden Torah will be revealed, as stated above. (Likutei Halachot, Hilchot Purim 4:5)