Yahya related to me from Malik from Nafi from Abdullah ibn Umar that Umar ibn al-Khattab said, "If a slave who has wealth is sold, that wealth belongs to the seller unless the buyer stipulates its inclusion."

Malik said, "The generally agreed upon way of doing things among us is that if the buyer stipulates the inclusion of the slave's property whether it be cash, debts, or goods of known or unknown value, then they belong to the buyer, even if the slave possesses more than that for which he was purchased, whether he was bought for cash, as payment for a debt, or in exchange for goods. This is possible because a master is not asked to pay zakat on his slave's property. If a slave has a slave-girl, it is halal for him to have intercourse with her by his right of possession. If a slave is freed or put under contract (kitaba) to purchase his freedom, then his property goes with him. If he becomes bankrupt, his creditors take his property and his master is not liable for any of his debts."

Muwatta Malik Book 31, Hadith 2