Philippians 4:21-22

For he who was called in the Lord while a slave, is the Lord's freedman; likewise he who was called while free, is Christ's slave. You were bought with a price; do not become slaves of men.

Ephesians 6:6-8

Not by way of eyeservice, as men-pleasers, but as slaves of Christ, doing the will of God from the heart. With good will render service, as to the Lord, and not to men, Knowing that whatever good thing each one does, this he will receive back from the Lord, whether slave or free.

1 Peter 2:16

Act as free men, and do not use your freedom as a covering for evil, but use it as bondslaves of God.