Musnad Ahmad 32:1407

'Isam ibn Khalid and Yunus ibn Muhammad narrated to us, they said: Al-'Attaf ibn Khalid narrated to us, from Zayd ibn Aslam, who said: We prayed Dhuhr with Umar ibn Abd al-Aziz, then we departed to Anas ibn Malik to ask about him, and he was ailing. When we entered upon him, we greeted him. He said: "Have you prayed?" We said: "Yes." He said: "O servant girl, bring me water for ablution. I have not prayed behind an imam after the Messenger of Allah (may Allah bless him and grant him peace) whose prayer was more similar to the prayer of the Messenger of Allah (may Allah bless him and grant him peace) than this imam of yours." 'Isam said in his narration: Zayd said: He did not mention Abu Bakr or Umar in that regard. Zayd said: And Umar used to perfect the bowing and prostration, and he would lighten the sitting and the standing.