Deuteronomy 15:16-17 -

It might happen, however, that the slave chose rather to remain with his master than to be manumitted, and in that case he was not to be forced to go free, which would be a hardship to him, but was to be, by a formal process of nailing his ear to the door of his master's house, constituted his slave for life (cf. Exodus 21:5 ). This was not a painful operation, especially as the servant's ear was probably already pierced for a ring; nor does any infamy appear to have been attached to the bearing of this badge of perpetual servitude. There is no mention here, as in Exodus, of the matter being referred to the judges; and this has led some to suppose that, by the time this later prescription was given, the earlier usage had passed away; but it is more natural to suppose that this usage was so regular and well known that it was needless formally to announce it.