Asim al-Ahwal عاصم الأحول · The Book of Mosques and Places of Prayer

I asked Anas whether Qunut was observed (by the Holy prophet) before ruku' or after ruku'. He replied: Before ruku'. I said: People conceive that the Messenger of Allah (ﷺ) observed Qunut after the ruku'. He said: The Messenger of Allah (ﷺ) observed Qunut (after the ruku' as the people conceive it) for a mouth invoking curse upon those persons who had killed men among his Companions who were called the reciter (of the Qur'an).

Never did I ace the Messenger of Allah (ﷺ) so much grieved (at the loss of a) small army as I saw him grieved at those seventy men who were called" reciters" (and were killed) at Bi'r Ma'una; and he invoked curse for full one month upon their murderers.