What is the ruling regarding one who prays while qat is in his mouth?

Summary of the Answer: It is not permissible for qat to remain in the mouth during prayer, as it goes against the humility (khushu') of prayer and because its presence in the mouth distracts the worshipper from the proper posture of prayer. It is considered disliked (makruh) by scholars and invalidates the prayer if any part of it descends into the stomach or if it spoils the recitation of Al-Fatiha.