How were the non-Hebrews expected to treat Hebrew slaves?
Leviticus 25:53 (ESV)
53He shall treat him as a worker hired year by year. He shall not rule ruthlessly over him in your sight.
The Hebrews were meant to protect their brothers from the mistreatment of non-Hebrew masters. These pagan masters were not to treat the Hebrews ruthlessly (pěrěḵ). See the commentary on Leviticus 25:43.
53 He shall treat him as a worker hired year by year. He shall not rule ruthlessly over him in your sight.