Musnad Ahmad 27:180

Isma'il ibn Ibrahim narrated to us, Hajjaj ibn Abi 'Uthman narrated to us, from Abu al-Zubayr, from 'Awn ibn 'Abd Allah ibn 'Utbah, from Ibn 'Umar, who said: While we were praying with the Messenger of Allah (peace and blessings of Allah be upon him), a man among the people said: "Allah is the Greatest, [much] greater, and praise be to Allah in abundance, and glory be to Allah morning and evening." The Messenger of Allah (peace and blessings of Allah be upon him) said: "Who is the one who said such and such?" A man from the people said: "I am, O Messenger of Allah." He said: "I was amazed by them; the gates of the heaven were opened for them." Ibn 'Umar said: "I have not abandoned them since I heard the Messenger of Allah (peace and blessings of Allah be upon him) say that."