Sahih Muslim Book - 4, Hadith - 968

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ وَأَبُو كُرَيْبٍ قَالَا حَدَّثَنَا أَبُو مُعَاوِيَةَ عَنْ الْأَعْمَشِ عَنْ الْمُسَيَّبِ بْنِ رَافِعٍ عَنْ تَمِيمِ بْنِ طَرَفَةَ عَنْ جَابِرِ بْنِ سَمُرَةَ قَالَ خَرَجَ عَلَيْنَا رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَقَالَ مَا لِي أَرَاكُمْ رَافِعِي أَيْدِيكُمْ كَأَنَّهَا أَذْنَابُ خَيْلٍ شُمْسٍ اسْكُنُوا فِي الصَّلَاةِ قَالَ ثُمَّ خَرَجَ عَلَيْنَا فَرَآنَا حَلَقًا فَقَالَ مَالِي أَرَاكُمْ عِزِينَ قَالَ ثُمَّ خَرَجَ عَلَيْنَا فَقَالَ أَلَا تَصُفُّونَ كَمَا تَصُفُّ الْمَلَائِكَةُ عِنْدَ رَبِّهَا فَقُلْنَا يَا رَسُولَ اللَّهِ وَكَيْفَ تَصُفُّ الْمَلَائِكَةُ عِنْدَ رَبِّهَا قَالَ يُتِمُّونَ الصُّفُوفَ الْأُوَلَ وَيَتَرَاصُّونَ فِي الصَّفِّ.

It was narrated that Jabir bin Samurah said: "The Messenger of Allah (s.a.w) came out to us and said: 'Why do I see you raising your hands like the tails of restless horses? Be calm when in prayer.' Then he came out to us and saw us sitting in circles. He said: 'Why do I see you in separate groups?' Then he came out to us and said: 'Why do you not make your rows as the Angels make their rows in the presence of their Lord?' We said: 'O Messenger of Allah, how do the Angels make their rows in the presence of their Lord?' He said: 'They complete the first rows and they keep close together in the rows."'