Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "Whoever frees his share in a slave, the freeing of the rest of the slave is his responsibility, if he has wealth, for Allah has no partner."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العتق / 21334