Maliks Muwatta Book 38, Hadith Number 10.
Section : Slaves Permitted to be Freed when a Slave must be Freed by Obligation.
Malik related to me that he had heard that al-Maqburi said that Abu Hurayra was asked whether a man who had to free a slave, could free an illegitimate child to fulfil that obligation. Abu Hurayra said, “Yes. That will give satisfaction for him.”