Sahih Muslim
The Book of Divorce (Kitab Al-Talaq)
Book Number: 009 / Hadith Number: 3580
Abu Huraira (Allah be pleased with him) reported Allah's Messenger (may peace be upon him) as saying: The slave who is jointly owned by two persons, and is emancipated by one of them, (this one) has liability (upon him to secure complete freedom for that slave).