1 Corinthians 7:21-22

7:21 Were you called as a slave? Do not worry about it. But if indeed you are able to be free, make the most of the opportunity. 7:22 For the one who was called in the Lord as a slave is the Lord’s freedman. In the same way, the one who was called as a free person is Christ’s slave.

Ephesians 6:8

6:8 because you know that each person, whether slave or free, if he does something good, this will be rewarded by the Lord.