Musannaf Ibn Abi Shayba 18:610

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: I heard Sufyan saying: The crime of the *mudabbar* (a slave promised freedom upon his master's death) is upon his master; he guarantees his value. Ibn Abi Layla said regarding the *mudabbar*: Upon him is the entirety of the crime.