It is narrated from Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever frees a slave for the sake of Allah, Allah Almighty will free, for every limb of the slave, a limb of the one who freed him from the Fire."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5818