Leviticus 25:42
For they are my servants, whom I brought out of the land of Egypt; they shall not be sold as slaves.
Leviticus 25:55
For it is to me that the people of Israel are servants. They are my servants whom I brought out of the land of Egypt: I am the LORD your God.
Romans 6:22
But now that you have been set free from sin and have become slaves of God, the fruit you get leads to sanctification and its end, eternal life.
1 Corinthians 7:21-23
Were you a slave when called? Do not be concerned about it. (But if you can gain your freedom, avail yourself of the opportunity.)