John 13:12-17 (ESV)
12 When he had washed their feet and put on his outer garments and resumed his place, he said to them, “Do you understand what I have done to you? 13 You call me Teacher and Lord, and you are right, for so I am. 14 If I then, your Lord and Teacher, have washed your feet, you also ought to wash one another’s feet. 15 For I have given you an example, that you also should do just as I have done to you. 16 Truly, truly, I say to you, a servant  is not greater than his master, nor is a messenger greater than the one who sent him. 17 If you know these things, blessed are you if you do them.