Friday of the Muslim week and the special noon service on Friday that all adult, male, free Muslims are obliged to attend. The jumʿah, which replaces the usual noon ritual prayer (ṣalāt aẓ-ẓuhr), must take place before a sizable number of Muslims (according to some legal scholars, 40) in one central mosque in each locality.

Muḥammad's choice of Friday as the Muslim day of communal worship was probably based on the pre-Islāmic function of Friday as market day, a natural occasion for dispersed local tribes to gather in a central location. The influence of the Jewish and Christian sabbath was also felt in the institutionalization of the Muslim Friday, though in Islām it was not a day of rest but a convenient setting for the special religious service. In the modern period, however, most Muslim countries have designated Friday as the legal day of rest; Turkey, following Western tradition, has made Sunday the holiday.