Musnad Abu Ya'la al-Mawsili 248:33

On the authority of Jabir ibn Samurah, he said: The Messenger of Allah (peace and blessings of Allah be upon him) entered the mosque and said: "Will you not form rows as the angels form rows before their Lord?" They said: "O Messenger of Allah, and how do they form rows before their Lord?" He said: "They complete the first rows and they stand close together in the row." He said: And he went out to the mosque while they were in the mosque in circles, so he said: "Why do I see you in separate groups?"