Musnad Abu Ya'la al-Mawsili 135:4

Abu Bakr ibn Abi Shaybah and Zuhayr ibn Harb narrated to us—and the wording is Zuhayr’s—[who said]: Abu Mu’awiyah narrated to us, from ‘Asim, from Anas, who said: I asked him about the Qunut: [is it] before the bowing or after the bowing? He said: Before the bowing. I said: Indeed, some people claim that the Messenger of Allah (may Allah bless him and grant him peace) performed Qunut after the bowing. He said: The Messenger of Allah (may Allah bless him and grant him peace) only performed Qunut for a month, supplicating against people who had killed some of his companions who were called "the Qurra" (the Reciters).