What are the boundaries of 'awrah (intimate parts) that invalidate prayer if uncovered, with details regarding a woman's 'awrah and the scholars' opinions concerning it?

The awrah (private parts) of a free woman in prayer is her entire body except for her face and hands. Her feet are also awrah according to the soundest opinion. The awrah of a man is what is between his navel and his knee.

If something from the awrah is uncovered during prayer unintentionally, the Shafi'is hold that the prayer becomes invalid unless it is covered immediately. The Hanbalis excuse a small amount that is not excessive. The Hanafis hold that the prayer becomes invalid if a quarter of a limb is uncovered for the duration of performing a rukn (pillar). As for exposure that occurs concurrently with the start of the prayer, it prevents the prayer from being valid if the uncovered part is a quarter of a limb. The most cautious approach is that adopted by the Shafi'is.