What should occupy a worshipper during their prayer, and should they supplicate to Allah with their heart or with their tongue?

The intention (niyyah) is a condition for the validity of prayer (ṣalāh); its place is the heart. It is the resolve to perform the act of worship as an act of drawing closer to Allah Almighty. It involves distinguishing between acts of worship and intending the one for whom the act is performed (for the sake of Allah). Uttering the intention verbally is not prescribed; rather, it is an innovation (bid'ah).

As for what should be contemplated during prayer, it is to remember the greatness of Allah, to have humility (khushū‘), and to reflect upon the prescribed sayings and invocations (adhkār) in each position, striving to recite the supplications reported from the Prophet (peace be upon him).

Supplication (du‘ā’) in the sense of asking Allah Almighty is made during prostration (sujūd) after the prescribed remembrance. However, the entire prayer is an act of worshipful supplication, meaning devotion and humility to Allah, and not merely a supplication of asking.

The advice is to adhere to the Sunnah of the Prophet (peace be upon him) in prayer and to reflect upon the Quran and the invocations to achieve its ultimate purpose, which is: "Indeed, prayer prohibits immorality and wrongdoing."