John 13:12-15:
After washing their feet, Jesus put his clothes back on and returned to the table. He said to them, “Do you understand what I have done for you? You call me “Teacher,” and “Sovereign”–and rightly, for so I am. If I, then—your Teacher and Sovereign—have washed your feet, you should wash each other’s feet. I have given you an example, that you should do as I have done to you.”