Muwatta Imam Malik (Riwayat Yahya)

Imam Malik, may Allah have mercy on him, said that if several slaves are contracted as mukatab (contracted for emancipation) in a single agreement, the master cannot free one of the slaves unless the other mukatab slaves agree. If they are minors, their consent is not considered. The reason for this is that among several slaves, one slave may be very clever and hardworking, and it is expected that through his labor and effort, he may also secure the freedom of the others. The master might then free only that person so that the remaining slaves, being unable to work as hard, would remain slaves. This is not permissible, because it causes harm to the remaining slaves, and the Messenger of Allah, peace and blessings be upon him, said: "There is no harm in Islam."