Does delaying sniffing the wind after feeling movement in the anus during the Tashahhud invalidate the prayer, or should one complete the recitation and only interrupt the prayer upon sensing the smell, especially since breathing is often oral during prayer, which makes smelling difficult?

If a worshipper doubts that something has exited from his posterior, he should not stop his prayer until he is certain of it, either by hearing a sound or smelling an odor. This is the figurative meaning of being certain of the impurity. The criterion is the certainty of the impurity's exit by any means, not necessarily by hearing or smelling. Therefore, whoever feels a movement in the posterior but does not smell an odor or is not certain that something has exited, should continue his prayer, and there is nothing against him. He is not obliged to search or investigate for an odor, as that may lead to waswasah (obsessive whispering).