Musnad Abu Ya'la al-Mawsili 42:237

Zuhayr narrated to us, Abd al-Samad narrated to us, Hammam narrated to us, Qatadah narrated to us, from Abu Nadrah, from Abu Sa’id, who said: Our Prophet, may Allah bless him and grant him peace, commanded us to recite the Opening of the Book (al-Fatihah) and whatever is made easy.