Literal meaning is: ‘announcement;’ in Islam, it refers to a specific set of phrases recited at the time of prayer to call the Muslims to perform one of the five daily prayers. It can be recited by the person who is performing one’s prayer individually, or it can be to call others to pray in congregation. The phrases of adhān are: 

Allāhu Akbar x 4

Ashhadu an lā ilāha illā Allāh x 2

Ashhadu anna Muḥammad ar Rasūl Allāh x 2

Ashhadu anna ʿAlī-yan walī Allāh x 2 (this phrase is not obligatory)

Ḥayya ʿalās salāh x 2

Ḥayya ʿalāl falāh x 2

Ḥayya ʿalā khayril ʿamal x 2

Allāhu Akbar x 2

La ilāha illā Allāh x 2

The line ‘Ashhadu anna ʿAlī-yan walī Allāh’ which acknowledges the position of Imām ʿAlī (ʿa) as Prophet Muḥammad’s (ṣ) successor is only recommended to recite.

Certain sects of Sunni Islam have different patterns of recitation.