After completing the Witr prayer, I remembered that I did not read the Qunoot supplication. Do I need to repeat it? Also, before ending the prayer with the Tasleem once, I was in doubt as to whether I read the Qunoot supplication or not, so I stood up and repeated that unit of prayer. Was that correct of me? My final question is whether the Witr prayer is obligatory or not. May Allaah reward you.

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger. 

We have previously underlined that the Witr prayer is a confirmed Sunnah and that it is not Fardh (obligatory), according to the majority of scholars, and that the Qunoot supplication is not Fardh either; rather, it is a recommended Sunnah, according to the majority of scholars, who held that it is prescribed, contrary to the Hanafis, who held that it is obligatory. Please refer to fatwas 83303 and 86832.

The Fiqh Encyclopedia reads:

“The scholars held four different opinions regarding the ruling on the Qunoot supplication in the Witr prayer:

Firstly, Abu Haneefah held that the Qunoot is obligatory in (the last unit of) the Witr prayer before the Rukoo’ (bowing) all year long (and not in Ramadhaan only). His two students, Abu Yoosuf and Muhammad, on the other hand, held that it is a Sunnah...

Secondly, the Maaliki scholars, in their more prevalent opinion, Taawoos, and a narration on the authority of Ibn 'Umar, may Allah be pleased with him, held that it is not prescribed to recite the Qunoot in the Witr prayer all year long. Tawoos said, ‘Qunoot in the Witr is a religious innovation...’

Thirdly, the preponderant view of the Shaafi‘is is that the Qunoot in the Witr prayer is recommended in the last half of Ramadhaan in particular...

Fourthly, the Hanbalis held that the Qunoot is an action from the Sunnah all year long in the last unit of prayer of the Witr prayer after the Rukoo’...” [briefly excerpted]

As you can see, the Qunoot is not Fardh according to all scholars. Only Abu Haneefah held that it is obligatory, while his two students (Abu Yoosuf and Muhammad) held that it is from the Sunnah. Some scholars even held that it is not prescribed in the first place.

In brief, you are not required to repeat the Witr prayer just because you did not recite the Qunoot supplication. It is wrong to add an extra unit of prayer to the Witr prayer because you doubt whether you said the Qunoot or not. Even if the praying person knows with certainty that he had missed the Qunoot before Tasleem, he may not stand up and perform an extra unit of prayer.

Allah knows best.