Forgetting to Recite the Du'aa Qunoot in the Witr salaah

Q: Salaah-670: what is the ruling when the Imaam proceeds into Ruku without reciting the Du'aa Qunoot in the Witr salaah?

Answer: The salaah will be valid if Sajiah Sahw is performed. While it is prohibited to recite the Du'aa Qurroot in Ruku or Qaumah, Sajdah Sahw will be necessary if this is done. If the Imaam stands up again after the Ruku, recites the Du'aa Qunoot and then repeats the Ruku, the second Ruku will not be taken into account (only the first). Therefore, the person who joins t5e Imaam in the second Ruku will not have joined this Rakaah. And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2