Answered by Shaykh Amjad Rasheed
According to my knowledge, the du`a of qunut in the dawn prayer is one of the main sunnas, and if one misses it, one has to prostrate for forgetfulness whether the omission was intentional or not. As it says in the `Umdah, a follower will only prostrate for forgetfulness in a group if the imam does something that calls for it, not if the follower does something that calls for it.
The recitation of the du`a of qunut is a main sunna in our school and most scholars concur on this. It is also one of the parts of the prayer that if one omits it, it is recommended to prostrate for forgetfulness for it and his prayer is not invalidated by that. So if one is a follower and the imam is differing from the madhhab by not reciting the du`a of qunut, it is then recommended for the follower to recite the du`a of qunut, even if the short way such that he say:
اِغفِر لِي يا غَفُور ، اللهُم صَلِّ على مُحَمدٍ وعَلَى آلِهِ وصَحبِهِ وسَلِّم.
Ighfir li ya Ghafoor, Allahumma salli `ala Muhammadin wa `ala aalihi wa sahbihi wa sallim.
This formula is sufficient to obtain the sunna and it is possible to recite this after standing from ruku` even if it is short.
The decided ruling in our school is that it is sunna for one whose imam omits the du`a of qunut to prostrate for forgetfulness, whether the follower himself recited it or not.
However, if performing the prostration of forgetfulness will cause fitna due to people’s ignorance of the differences of the imams and not exalting them and what they say, as is often the case today, then there is no harm in omitting the prostration as many scholars of our school do, for there is some ease in the matter.
Amjad Rasheed
[Translated by Sr. Shazia Ahmad]