Sahih Muslim 430 a
The Book of Prayers
The Command To Be Calm During The Prayer And The Prohibition Of Gesturing With One's Hand And Raising It When Saying The Salam; And Completing The First Rows, Aligning In Them, And The Command To Come Together
Jabir b. Samura reported: 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 Prophet) said: "They make the first rows complete and keep close together in the row."