Mishkat al-Masabih 1301

‘Abd ar-Rahman b. ‘Abd al-Qari said: I went out one night to the mosque with ‘Umar b. al-Khattab and we saw the people in sections separate from one another, one man praying by himself, and another followed by a group; so ‘Umar said, “If I collected these people behind one reciter it would be better.” He then made up his mind and collected them with Ubayy b. Ka‘b as imam. Afterwards I went out with him another night when the people were following the prayer of their reciter, and ‘Umar said, “This is a good innovation, but what you miss through sleeping is more excellent than what you are getting up for, meaning at the end of the night, for the people were getting up during the early part of the night.
Bukhari transmitted it.