A father and a son were once guests of Imam ‘Ali (as). As they arrived, Imam received them warmly and arranged for their comfortable accommodation. In a room where they were seated, Imam sat opposite them, engaging them in a friendly conversation.
And then it was time for the meal. After food had been served and eaten, Qambar, Imam's servant, brought a basin and a pitcher full of water for washing the guests' hands. Imam took the pitcher himself and asked the father to extend his hands so that he would pour the water.
“How is it possible that my Imam serves me? It should be otherwise,” the guest said.
Imam ‘Ali (as) said: “Here is your brother in faith, eager to serve his brother and to earn the pleasure of Allah. Why do you prevent him?”
But the guest hesitated. Finally Imam (as) said: “As your Imam, I request that you allow me the honour of this service.”
And when the guest complied, Imam said: “Let your hands be washed thoroughly. Do not hasten, thinking that I should be relieved of this duty early.”
When it was the son's turn, Imam instructed his own son Muhammad b. Hanafiyyah, to hold the pitcher and wash the guest's hands. Looking at his son, Imam said:
I washed your father's hands. My son washed your hands. If your father had not been my guest today, I would have washed your hands myself. But Allah loves to see that when a father and a son are present in a place, the father enjoys a privilege and a priority.