In each of the four surahs al-Sajdah, Fuṣṣilat, al-Najm, and al-ʿAlaq, there is a verse of sajdah,[1] which means that if one recites this verse or listens to it, he must immediately perform sajdah after the verse has finished. If he forgets to do this, he must perform sajdah whenever he remembers. Performing sajdah is not obligatory if one hears such a verse involuntarily, although it is better that he does.