Answered by Shaykh Faraz Rabbani
Situation A: A person is Shafi and does 1 rakat witrs for X number of years. This person becomes Hanafi and wants to make up missed prayers he has in the past. Do these witr prayers have to made up?
Situation B: A person is Shafi and doesn’t do any witr because its not wajib on them for X number of years. The person becomes Hanafi and wants to make up missed prayers he has in the past. Does he have to make up the witrs?
Walaikum assalam,
There is a legal principle that, “An ijtihad is not invalidated by another.” [Kasani, Bada’i` al-Sana’i` 7.6; Abd al-Aziz al-Bukhari, Kashf al-Asrar, 3.74; and almost every major Hanafi fiqh work, with similar wordings]
From this principle, a derived ancillary principle is that, “Following a valid ijtihad in the past does not need to be rectified by one’s following different ijtihad later on.”
As such, if the person prayed 1-rakat witr as a Shafi`i, or even omitted praying it, no makeup would be necessary if one later became a Hanafi.
Of course, if one chooses to make it up, out of caution or taqwa, one is rewarded. It is a sunna to makeup missed witrs in the Shafi`i and Hanbali schools. [cf: Ibn Hajar, Tuhfa al-Muhtaj; Buhuti, Kashshaf al-Qina`]
And Allah alone gives success.
Walaikum assalam,
Faraz Rabbani.
BTW: Ahlan wa Sahlan