Musnad Ahmad 32:1484

'Ali narrated to us, Humaid informed us, from Anas, who said: "Bilal performed the iqamah for the prayer, but a man intercepted the Messenger of Allah (peace and blessings of Allah be upon him). He kept him standing until some of the people became drowsy. Then the Messenger of Allah (peace and blessings of Allah be upon him) came and led the people in prayer."