Sahih Muslim Book 4, Hadith 130

The Messenger of Allah (ﷺ) came to us and said: "How is it that I see you lifting your hands like the tails of headstrong horses? Be calm in prayer." He (the narrator) said: He then again came to us and saw us (sitting) in circles. He said: "How is it that I see you in separate groups?" He (the narrator) said: He again came to us and said: "Why don't you draw yourselves up in rows as angels do in the presence of their Lord?" We said: Messenger of Allah, how do the angels draw themselves up in rows in the presence of their Lord? He (the Holy Prophet) said: "They make the first rows complete and keep close together in the row."