Mark 10:44

And whosoever of you will be the chiefest, shall be servant of all.

Cross-reference

1 Kings 12:7 advises a king to serve the people, providing an OT example of servant leadership.

Matthew 23:11 repeats the principle that the greatest must be servant, reinforcing the 'slave of all' command.

Philippians 2:7 describes Christ taking the form of a servant, providing the ultimate example of being a slave.