Mishkat al-Masabih #3812

‘Ali told that some slaves came out to God’s Messenger, i.e. on the day of al-Hudaibiya, before the peace was ratified, and their masters wrote to him saying, “We swear by God, Muhammad, that they have not gone out to you through desire for your religion, but they have done so only to fly from servitude.” Some people assured him they had spoken the truth and advised him to send them back to them, but God’s Messenger became angry and said, “I do not think you people of Quraish will cease till God sends someone to you who will cut off your heads for this.” He refused to send them back, saving they were God’s freedmen. Abu Dawud transmitted it.