Musannaf Ibn Abi Shayba 19:393

Abu Bakr narrated to us, he said: Abu Usama narrated to us, from Hisham, from al-Hasan, who said: If he declares himself a liar before the *li'an* (imprecation) is concluded, he is flogged, and she remains his wife. And if he declares himself a liar after the *li'an*, then there is nothing [to be done].