It was narrated that Abu Bakr as Siddeeq said:
The Messenger of Allah (ﷺ) said: “No one who mistreats his slaves will enter Paradise.` Aman said: O Messenger of Allah, didn't you tell us that this ummah is the greatest in numbers of slaves and orphans? He said: `Yes, so treat them kindly as you treat your children and feed them from what you eat.` They said: What could benefit us in this world, O Messenger of Allah? He said: “A good horse which you keep ready for fighting for the sake of Allah and a slave to take care of you. If he prays (becomes Muslim), then he is your brother, if he prays, then he is your brother.”