Musannaf Ibn Abi Shayba 3:4678

Al-Walid ibn 'Uqbah narrated to us, he said: Sufyan narrated to us, from Ibn Jurayj, from 'Ata', who said: Whoever considers the Qunut to be [a sunnah] and does not perform the Qunut, then upon him are two prostrations of forgetfulness.