Salamah bin Rawh bin Zinba' relates that his grandfather, Sayyiduna Zinba' (may Allah be pleased with him), had castrated a slave of his. Then that slave came to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) freed him because of the mutilation (muthlah: the wrong of cutting off limbs).
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5283