Musnad Ahmad 724:0

Narrated Rifa'ah ibn Rafi' al-Zuraqi: We were praying behind the Prophet (peace be upon him) one day. When he raised his head from bowing, he said, "Sami' Allahu liman hamidah" (Allah hears those who praise Him). A man behind him said, "Rabbana wa lakal-hamd, hamdan kathiran tayyiban mubarakan fihi" (Our Lord, and to You is the praise, abundant, good, and blessed praise therein). When he finished, he said, "Who spoke?" The man said, "I did." He said, "I saw more than thirty angels rushing to see which of them would record it first."