From Sahih Bukhari (Hadith 2504):
Narrated Abu Huraira:The Prophet (ﷺ) 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
Reference: Bukhari 2504