Exodus 12:44
But every man's servant, whom he has got for money, may take of it, when he has had circumcision.
Genesis 17:12-13
Every male among you, from one generation to another, is to undergo circumcision when he is eight days old, with every servant whose birth takes place in your house, or for whom you gave money to someone of another country, and not of your seed.
Genesis 17:23
And Abraham took Ishmael, his son, and all whose birth had taken place in his house, and all his servants whom he had made his for a price, every male of his house, and on that very day he gave them circumcision in the flesh of their private parts as God had said to him.