Musnad Ahmad 1153:1936

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from al-Zuhri, from 'Urwah, from 'Aishah, who said: "The Messenger of Allah (ﷺ) prayed one night in the mosque during the month of Ramadan, and there were people with him. Then he prayed the second [night], and more people gathered that night than the first. When it was the third or fourth [night], the mosque became full until it was crowded with its people, but the Messenger of Allah (ﷺ) did not come out to them. The people began calling out to him, 'The prayer!' but he did not come out. When morning came, 'Umar ibn al-Khattab said to him, 'The people kept waiting for you last night, O Messenger of Allah.' He said: 'Indeed, their matter was not hidden from me, but I feared that it would be made obligatory upon you.'"