What Should A Person Who Forgets To Recite Takbir In The Third Rakat Of Witr Prayer Do?

What should a person who forgets to recite takbir in the third rakat of witr prayer do?

If a person forgets the to recite takbir and the supplications of Qunut and remembers it after ruku, he does not go back to recite it (Kasani, Bada’i, I, 274). In that case, the prayer is completed by going down to sajdah al-sahw (prostration of forgetfulness) at the end of the prayer (Ala’uddin, Hadiyyat al-Alaiyya, p. 95).

Source: Presidency Of Religious Affairs The Turkey, High Board of Religious Affairs FATWA