Deuteronomy 23:15,16

The servant which is escaped from his master It seems, from the connection, that this has a particular relation to times of war, when heathen soldiers or servants might desert and come over to the Israelites with intent to turn proselytes to the true religion. In which case, they were neither to send them back, and expose them to the severity of their heathen masters, nor use them hardly themselves, but permit them to live peaceably, and with full enjoyment of all the liberties and privileges of a proselyte in Israel, Leviticus 19:33; Leviticus 19:35. It may be understood, likewise, of such foreign servants as, upon inquiry, appeared to be unjustly oppressed by their masters. For it is not strange if the great God, who hates all tyranny, and styles himself the refuge of the oppressed, should interpose his authority to rescue such persons from their cruel masters. He shall dwell with thee in the place which he shall choose This shows plainly that the passage is not to be understood of the servants of the Israelites their brethren, but of aliens and strangers; he is said to be escaped, and to be allowed to dwell among them, which the servant of an Israelite was supposed to do before.