John 13:5

5 After that he poureth water into a bason, and began to wash the disciples’ feet, and to wipe them with the towel wherewith he was girded.

The Holy Bible: King James Version, Electronic Edition of the 1900 Authorized Version. (Bellingham, WA: Logos Research Systems, Inc., 2009), Jn 13:5.

One of the greatest acts of humility would be to wash someones feet. Another one would be, submitting to having your feet washed by a loving brother you are at odds with.