Sahih Bukhari Volume 3, Book 46, Hadith Number 698.

Narated By ‘Abdullah bin ‘Umar : Allah’s Apostle said, “Whoever frees his share of a common slave and he has sufficient money to free him completely, should let its price be estimated by a just man and give his partners the price of their shares and manumit the slave; otherwise (i.e. if he has not sufficient money) he manumits the slave partially.”