Sahih Bukhari Volume 3, Book 44, Hadith Number 682.

Narated By Abu Huraira : The Prophet said, “Whoever manumits his share of a jointly possessed slave, it is essential for him to manumit the slave completely if he has sufficient money. Otherwise he should look for some work for the slave (to earn what would enable him to emancipate himself), without overburdening him with work.”