Musnad Ahmad 1148:2

'Abd al-Samad narrated to us, Mulazim ibn 'Amr narrated to us, 'Abd Allah ibn Badr narrated to us, that 'Abd al-Rahman ibn 'Ali narrated to him, that his father 'Ali ibn Shayban narrated to him, that he said: I prayed behind the Messenger of Allah, peace and blessings of Allah be upon him. He turned away and saw a man praying alone behind the row. The Prophet of Allah, peace and blessings of Allah be upon him, stood until the man finished his prayer. Then he said to him: "Restart your prayer, for there is no prayer for one who is alone behind the row."