The evidence for leaving the prayer if one becomes aware of impurity during the prayer?

The questioner : Yes. One must leave the prayer if he becomes aware of the impurity during the prayer.

The Shaykh : Yes. And he is unable to remove the towel. The evidence is that removing impurity is a condition for the validity of the prayer. Yes. The evidence is the command of the Prophet (peace and blessings be upon him) to the menstruating woman: when menstruation affects her clothes, he ordered her to cut it off, then wash it with water, then pray in it. The fact that he ordered her to purify the garment and then pray in it indicates that the purity of the garment is necessary. Now, this man entered the prayer thinking his garment was pure and did not know of its impurity, but then he became aware of it. He is now wearing a garment that requires purification, and he cannot purify it now. So we say he must exit the prayer and restart it.