Musnad Ahmad 30:1826

Qutaybah narrated to us, he said: Abd al-Aziz ibn Muhammad narrated to us, from Muhammad ibn Tahla’, from Muhsin ibn Ali, from Awf ibn al-Harith, from Abu Hurayrah, he said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Whoever performs wudu and perfects his wudu, then goes out and finds that the people have already prayed, Allah will give him the like of the reward of the one who prayed it or attended it, without that diminishing anything from their rewards."