Musnad Abu Ya'la al-Mawsili 115:241

Abu Khaythama narrated to us, Waki' narrated to us, Hisham al-Dastawa'i and Sa'id bin Abi 'Aruba narrated to us, from Qatada, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) only performed the Qunut for a month after the bowing.