The ruling on the prayer of one whose thigh or knee is exposed

Question:
May Allah reward you, Honorable Shaykh. The questioner asks: If a man prays in short trousers that expose his knee, is his prayer invalid if his knee or part of his thigh becomes visible?

Answer:
Yes, because he did not cover his 'awrah (the part of the body that must be covered). Covering the 'awrah is a condition for the validity of the prayer. A man's 'awrah is the area between the navel and the knee; the navel is included in the 'awrah, and the knee is included in the 'awrah. Yes.