Musnad Ahmad 1220:1

Waki' narrated to us, he said: Umm Ghurab narrated to me, from a woman who is called 'Aqilah, from Salamah bint al-Hurr, she said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "A time will come upon the people when they will stand for an hour, not finding an Imam to lead them in prayer."