If a person has Qaza-e-Umri for like 12 years and it is difficult for him to pray one extra qaza salat with each regular prayer. Can such a person omit the sunnan (muakkidah and ghair muakkidah) of regular salat and pray the qaza salat.
A person who has Qadhaa-e-Umri to fulfil may leave out the Sunnah Ghair-e-Muakkadah and read his Qadhaa in place of it. For example, the 4 Rakaats Sunan Ghayr-e-Muakkadah before Esha and before Asr can be substituted with the Qadhaa Salaat. A person cannot leave out the Sunan-e-Muakkadah in order to fulil his Qadhaa-e-Umri, because in Shari’ah the Sunan-e-Muakkadah are as important as a Waajib and a person will be sinful if he omits it. (Aalamgiri vol.1 pg.125)
An easy method to fulfil the Qadhaa-e-Umri is to read one Qadhaa Salaat with every Fardh Salaat. For example, at the time of Fajr one should read Qadhaa of one Fajr and likewise for every Salaat. In this manner, a person can fulfil his Qadhaa-e-Umri without it being too burdensome on him.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai