Musannaf Ibn Abi Shayba 19:820

Abu Bakr narrated to us, he said: Waki' narrated to us, from Ibn 'Awn, he said: I asked al-Hasan and Ibn Sirin about a man who slanders a man, then he (the victim) forgives him. Al-Hasan said: "No." And Ibn Sirin said: "I do not know."