Mishkat al-Masabih 877
Rifa'a b. Raf’i said:
We were praying behind the Prophet, and when he raised his head at the end of the rak'a he said, “God listens to him who praises Him.” A man behind him said, ‘O our Lord, to Thee be the praise, abundant, good, blessed, sufficient.” When he ended he asked, “Who was the speaker just now ?” and when the man replied that he had spoken he said, “I saw over thirty angels racing one another to be the first to record it.” 

Bukhari transmitted it.
وَعَنْ رِفَاعَةَ بْنِ رَافِعٍ قَالَ: كُنَّا نُصَلِّي وَرَاءَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَلَمَّا رَفَعَ رَأْسَهُ مِنَ الرَّكْعَةِ قَالَ: «سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ» . فَقَالَ رَجُلٌ وَرَاءَهُ: رَبَّنَا وَلَكَ الْحَمْدُ حَمْدًا كَثِيرًا طَيِّبًا مُبَارَكًا فِيهِ فَلَمَّا انْصَرَفَ قَالَ: «مَنِ الْمُتَكَلِّمُ آنِفًا؟» قَالَ: أَنَا. قَالَ: «رَأَيْتُ بِضْعَةً وَثَلَاثِينَ مَلَكًا يَبْتَدِرُونَهَا أَيُّهُمْ يَكْتُبهَا أول» . رَوَاهُ البُخَارِيّ