It was narrated from Salamah bin Rawh bin Zinba', that :
his grandfather came to the Prophet (ﷺ) and he had castrated a slave of his. The Prophet (ﷺ) manumitted the slave in compensation for having been mutilated. (ID)
English reference (ID): Vol. 3, Book 21, Hadith 2679 (ID)
Arabic reference (ID): Book 21, Hadith 2781 (ID)