Musnad Abu Ya'la al-Mawsili 148:14

Ishaq ibn Abi Isra'il narrated to us, Mu'adh ibn Mu'adh narrated to us, Sulayman al-Taymi narrated to us, from Abu Mijlaz, from Anas: That the Messenger of Allah (may Allah bless him and grant him peace) performed Qunut for a month, supplicating against Ri'l and Dhakwan.