How does a Mukatab (a slave contracted for manumission) acquire and manage wealth earned during his servitude?

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Whatever the Mukatab acquires from the installments (Nujum) of his Kitabah, whether through labor or other means, he gains ownership of it upon taking possession, and a full lunar year must pass (before Zakat is due on it). This is because his possession of what is in his master's hands is incomplete. Consequently, usury (Riba) is permissible between them. No Zakat is due on the debt owed by the Mukatab, as his ownership over that money is not complete; thus, a full year must pass after he takes possession of money acquired from others, similar to receiving money from a stranger.