Verses 12 to 17 of John 13. 

After washing their feet, he put on his robe again and sat down and asked, “Do you understand what I was doing? You call me ‘Teacher’ and ‘Lord,’ and you are right, because that’s what I am. And since I, your Lord and Teacher, have washed your feet, you ought to wash each other’s feet. I have given you an example to follow. Do as I have done to you. I tell you the truth, slaves are not greater than their master. Nor is the messenger more important than the one who sends the message. Now that you know these things, God will bless you for doing them.