What was done to a Hebrew servant who chose to stay with his master for life?

Answer: His ear was pierced with an awl

If a servant loved his master and chose to stay, an awl was pierced through his ear into the door, and he served for life.

“But if your servant says to you, ‘I do not want to leave you,’ because he loves you and your household and is well off with you, then take an awl and pierce it through his ear into the door, and he will become your servant for life. And treat your maidservant the same way.”— Deuteronomy 15:16-17 (BSB)