The worshipper must have the intention of praying the prayer for which he is standing. He must have the intention in his heart of performing a specific prayer, such as the fard (obligatory prayer) of Zuhr or of ‘Asr, or the Sunnah of those prayers. This is a condition or pillar (essential part) of the prayer, but uttering the intention verbally is a bid’ah which goes against the Sunnah, which was not suggested by any of the imams who are followed.
