הלכה על קידושין 47:6

The commandment of work with a Canaanite slave forever: That we have a Canaanite slave work forever, meaning that we should never manumit him; and he should only go free for [suffering the loss of] a tooth or limb, as it appears in Scripture (Exodus 21:26-27) - or from the main limbs that are similar to them, meaning limbs that do not grow back, as the accepted traditional explanation comes about this (Kiddushin 24a) - as it is stated (Leviticus 25:46) "you shall work them forever." And they, may their memory be blessed, said (Gittin 38a), "Rav Yehudah said, 'Anyone who manumits his slave is in violation of a positive commandment, as it says, "you shall work them forever."'" And [any] one from all of the [other] nations who was acquired by a Jew as a slave is called a Canaanite slave. But all slaves are attached with the name, Canaan, because Canaan was cursed to be a slave - he and his progeny - forever. And even though this section in which we were commanded to subjugate them is speaking about Canaanites - as it is written (Leviticus 25:44), "from the peoples that surround you may you purchase a slave or maid-servant," and it is written earlier (Leviticus 25:38), "to give to you the Land of Canaan" - it was known to the Sages, may their memory be blessed, that it was not only Canaan and those in their land that were called Canaanite slaves. As the law is the same for all the rest of the nations - that they have the status of a Canaanite slave in every matter.