Is the prayer of one who frequently experiences flatulence valid if he holds back the wind during prayer, and is it permissible to hold it back during Tawaf?

The prayer of one who is resisting the urge to relieve oneself of the two impurities (urine or feces) or gas is valid according to the majority of scholars, even though performing it is disliked due to the Prophet's (peace be upon him) prohibition of such. If the resistance is slight and does not affect one's devotion (khushu'), there is no harm in praying. However, if it is strong and affects one's devotion, it is better to relieve oneself first and then pray, even if it means missing the congregational prayer, because maintaining devotion in prayer is more important.