Musannaf Ibn Abi Shayba 19:221

Abu Bakr narrated to us, he said: Ghundar narrated to us, from Shu'bah, from Mansur, from Ibrahim, from Ali: Regarding the *mukātab* (a slave who has a contract of manumission), if he commits a crime requiring a prescribed punishment (*hadd*), he said: He is to be flogged according to the extent of what he has paid [of his manumission price].