Another narration is: "He is guilty of disbelief (i.e., in case he believes in the lawfulness of doing so)."
Commentary: The institution of slavery does not exist in the modern world, but if it exists anywhere or a situation arises in which it re-emerges, the principle stated in this Hadith will be applicable. The Hadith also makes it clear that if someone has expressed his commitment to serve somebody, he should not back out. It also urges us to show gratefulness to one's benefactors and to reciprocate the good, one receives.