Exodus 21:2-11, 26-27

In the Bible, if a woman is sold into slavery, the presumption was that she was to become someone's concubine--whether the master's, his son's, or another servant's--but that wasn't a given. Sometimes she would be a temporary laborer or a woman's personal servant (aka "handmaid").

A concubine was a wife who had been purchased as a slave. She had rights and was legally recognized as a man's wife, but that didn't nullify her status as his slave (which probably had inheritance implications for her firstborn son). As a bare minimum, a man owes three things to a concubine: food, clothing, and procreation. A concubine is allowed an unquestioned divorce if her husband doesn't meet his obligations to her.

If a man buys her to be a wife and then changes his mind, he must allow her to be redeemed by her family. V8 says he can't sell her to a foreigner, but this means anyone outside of her family, not just people from another nation. If a man buys a slave girl to marry his son, he must treat her as his own daughter. He can't treat her as a slave.

In God's Law, even slaves must be treated humanely. Biblical slavery was nothing like the slavery perpetrated in many other cultures even today.