Musannaf Ibn Abi Shayba 3:4603

Mu'adh ibn Mu'adh narrated to us, from al-Taymi, from Abu Mijlaz, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) only performed Qunut in the morning prayer for a month, supplicating against [the tribes of] Ri'l and Dhakwan.