Sayyiduna Ibn Umar (may Allah be pleased with them both) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Whoever frees his share in a slave, it is his responsibility to free the whole slave if he has wealth equal to his price; otherwise, only as much is freed as he has freed."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العتق / 21360