Sahih Muslim
The Book of Oaths (Kitab Al-Aiman)
Book Number: 015 / Hadith Number: 4106
Salim b. 'Abdullah reported on the authority of his father that Allah's Apostle (may peace be upon him) said: He who emancipates a slave (shared) by him and another one, his full price may be justly assessed from his wealth, neither less nor more, and he (the slave) would be emancipated if he (the partner) would be solvent enough (to forgo the amount of his share).