Musannaf Ibn Abi Shayba 19:406

Abu Bakr narrated to us, he said: Mu'tamir narrated to us, from Layth, from Tawus, Mujahid, and al-Hakam, from Ibrahim and al-Sha'bi, regarding a man who has a slave woman under him and he accuses her of adultery (qadhf): They said: There is no *li'an* (imprecation) between them, and there is no prescribed punishment (*hadd*) upon the one who accuses her.