Musannaf Ibn Abi Shayba 19:396

Abu Bakr narrated to us, he said: Shareek narrated to us, from Mughira, from Ibrahim; and from Layth, from Mujahid; and from Jabir and Ibn Salim, from Amir, they said: Whoever accuses the son of a woman involved in *li'an* (imprecation) [of illegitimacy], he shall be lashed.