Sahih Bukhari Volume 003, Book 044, Hadith Number 671.

Narated By Nafi : Ibn 'Umar said, "Allah's Apostle said, 'If one manumits his share of a jointly possessed slave, and can afford the price of the other shares according to the adequate price of the slave, the slave will be completely manumitted; otherwise he will be partially manumitted.' " (Aiyub, a sub-narrator is not sure whether the saying"... otherwise he will be partially manumitted" was said by Nafi' or the Prophet.)