Musnad Ahmad 30:2402

Yahya ibn Sa'id narrated to us, from Ja'far ibn Maymun, who said: Abu 'Uthman al-Nahdi narrated to us, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) commanded him to go out and proclaim: "There is no prayer except with the recitation of the Opening of the Book (Al-Fatihah), and what is more."