Musannaf Ibn Abi Shayba 19:397

Abu Bakr narrated to us, he said: Abd al-Salam narrated to us, from Layth, from Mujahid and Tawus, regarding the man who says to the son of the woman involved in *li'an* (imprecation), "O son of the adulteress." They both said: He shall be lashed eighty times.