The author of this book stated: If someone forgets the Qunoot until they bow (ruku'), they should perform the Qunoot when they raise their head from the bowing position. However, Imam Al-Sadiq عليه السلام, prohibited this for Witr and Fajr (Dawn) prayers, differing from the general practice of the public, as they perform Qunoot after the bowing. He permitted this for other prayers because the majority of the public do not see Qunoot as necessary in them. When a person completes the Witr prayer, they should proceed to pray the two rak'ahs of Fajr.
Commentary #3