Deuteronomy 15:16-17

16But perhaps your servant will say to you, ‘I do not want to leave you!’ He may say that because he loves you and your family. He enjoys his life with you.

17If he says that, you must take a tool with a sharp point. Push it through his ear, into your door. After that, he will be your servant for his whole life. Do the same thing for any female servant who wants to stay with you.