What should one do if the congregation begins while one is praying the sunnas?

Question

If someone is praying a sunna or a nafl in the front row and the congregation of the fard stands up, does the prayer of those praying the sunna or nafl not count, as is commonly held?

Answer

The prayer does not become fasid (invalid); however, he should complete his sunna or nafl lightly and then join the congregation.

Source: Fatawa Mahmudiyya

Preview. The full text opens with JavaScript enabled.