Musnad Ahmad 27:663

Yunus ibn Muhammad narrated to us, Marthad—meaning Ibn Amir al-Huna'i—narrated to us, Abu 'Amr al-Nadbi narrated to me, 'Abdullah ibn 'Umar ibn al-Khattab narrated to me, he said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Indeed, Allah marvels at the prayer in congregation."