The World Federation One Stop Fiqh

Ruling 972

In recommended prayers, it is not necessary to recite the other surah even if that prayer has become obligatory on account of a vow. However, in some recommended prayers, such as the prayer of loneliness (ṣalāt al‐waḥshah), that require a specific surah to be recited, if one wants to act according to the rules of that prayer, he must recite the specified surah.