Deuteronomy 15:15-19

And you are to remember that you were a slave in the land of Egypt, and the Lord your God redeemed you; therefore I am commanding this of you today.

But it shall come about, if he says to you, ‘I will not leave you,’ because he loves you and your household, since he is doing well with you,

then you shall take an awl and pierce it through his ear into the door, and he shall be your servant permanently. You shall also do the same to your female slave.

“It shall not seem difficult for you when you set him free, because he has given you six years with double the service of a hired worker; so the Lord your God will bless you in whatever you do.

“You shall consecrate to the Lord your God all the firstborn males that are born in your herd and in your flock; you shall not work with the firstborn of your herd, nor shear the firstborn of your flock.