What is the ruling on the prayer of one who realizes that the intention was absent during its performance?

Scholars unanimously agree on the obligation of intention (niyyah) for prayer, and that it is not valid without it. It is permissible to make the intention a short time before the takbirat al-ihram (the opening takbir), though aligning it with the takbir is better. If the worshipper makes the intention for prayer, then their prayer is valid, even if they lose awareness of the intention during the prayer, as long as they made it at the beginning. If they do not make the intention for prayer, then their prayer is invalid by the consensus of scholars. The place of the intention is the heart. Humility (khushu') in prayer is a Sunnah, and its absence does not invalidate the prayer. One should not pay attention to the whispers of Satan.