Musnad Ahmad 32:2007

Al-Aswad ibn Amir narrated to us, Shu'bah narrated to us, from Qatadah, from Anas: "The Prophet, peace and blessings of Allah be upon him, performed Qunut for a month, cursing Ri'l, Dhakwan, and Usayyah, for they disobeyed Allah and His Messenger."