Mishkat al-Masabih 1091
Jabir b. Samura said:
God’s Messenger came out to us and when he saw us sitting in circles he said, “How is it that I see you in separate companies?” On another occasion he came out to us and said, “Why do you not draw yourselves up in rows as the angels do in the presence of their Lord?” We asked, "Messenger of God, how do the angels draw themselves up in rows in the presence of their Lord?” He replied, "They make the first rows complete and keep close together in the row.” 

Muslim transmitted it.
وَعَنْ جَابِرِ بْنِ سَمُرَةَ قَالَ: خَرَجَ عَلَيْنَا رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَرَآنَا حلقا فَقَالَ: «مَالِي أَرَاكُمْ عِزِينَ؟» ثُمَّ خَرَجَ عَلَيْنَا فَقَالَ: «أَلَا تَصُفُّونَ كَمَا تَصُفُّ الْمَلَائِكَةُ عِنْدَ رَبِّهَا؟» فَقُلْنَا: يَا رَسُولَ اللَّهِ وَكَيْفَ تَصُفُّ الْمَلَائِكَةُ عِنْدَ رَبِّهَا؟ قَالَ: «يُتِمُّونَ الصُّفُوفَ الْأُولَى وَيَتَرَاصُّونَ فِي الصَّفّ» . رَوَاهُ مُسلم