Through the same chain, it is narrated from Sayyiduna Samurah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) used to give a command concerning the slaves of a man or woman that are his own personal property and serve his work, and whom he does not wish to sell: he (peace and blessings be upon him) used to command us not to pay any charity on their behalf, and he used to command us to pay the zakah on slaves who are kept for trade.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 7017