What is the ruling on the prayer of one who intentionally thinks during it?

Deliberate thinking during prayer detracts from its completeness and reduces the reward. Scholars have unanimously agreed that whoever occupies their heart and mind with matters other than prayer will have a diminished reward and lose the perfection of prayer. Nevertheless, mere thinking does not invalidate the prayer unless it completely distracts the worshipper to the point where they do not know what they have prayed; in such a case, jurists differ regarding its invalidity. Prayer is considered valid, by widely accepted consensus, even with thoughts and the mind being occupied with other matters. Some jurists have indicated that the reward decreases according to the level of inattentiveness. Al-Ghazali held the consensus that prayer is valid if the worshipper knows the number of its rak'ahs, its pillars, and its conditions, even if they are not devout. As for the work of the heart, the correct view within the madhhab is that it does not invalidate the prayer even if prolonged, though some say it does if prolonged. According to the first view, the worshipper is only rewarded for what they did with their heart.