Musnad Abu Ya'la al-Mawsili 2:92

Abu Hisham narrated to us, al-Nadr—meaning Ibn Mansur—narrated to us, Abu al-Janub narrated to us, he said: I saw Ali drawing water for his ablution, so I hastened to draw it for him. He said: "Desist, O Abu al-Janub, for I saw Umar drawing water for his ablution, and I hastened to draw it for him. He said: 'Desist, O Abu al-Hasan, for I saw the Messenger of Allah (may Allah bless him and grant him peace) drawing water for his ablution, and I hastened to draw it for him. He said: Desist, O Umar, for I dislike that anyone should share with me in my purification.'"