In these verses of the bible. Rules are laid down for the treatment of slaves. According to the bible, not only are you allowed to keep slaves, but you are allowed to beat them with rods. You are also allowed to beat them to death provided it takes them longer than "a day or two" to die. It does say however that if you permanently blind them or bash their teeth out, that you will have to let them go.

Exodus 21:20-21 and Exodus 21:26-27