I say, and with God's success: If there is impurity the size of a dirham on him and he prays with it, his prayer is valid, and it is excused. However, if the impurity is more than the size of a dirham, then it is not excused. The allowance is for the size of a dirham because the one who used stones for cleaning instead of water has his prayer accepted by consensus, and stones do not completely remove impurity. Therefore, if he sits in a small amount of water, it becomes impure, indicating that it is excused and measured by the dirham. Moreover, a small amount of impurity is excused due to hardship, like the dripping of urine, similar to the heads of pins. Necessity includes the private parts and others, so it is excused due to hardship. The term 'the size of a dirham' refers to the thick impurity: the weight of a dirham — which is a mithqal. And for the thin impurity: the area of a dirham — which is about the width of the palm, specifically the concave width of the palm, which is within the joints of the fingers. They measured it by the size of a dirham based on the place of cleaning, as the area of cleaning is excused. Ibrahim al-Nakha'i said: "They meant to say the size of the seat, but they found it inappropriate to mention that in their gatherings, so they referred to it as the dirham." See: Al-Kasani, Bada'i' al-Sana'i, 1/80, and Tabyin al-Haqaiq, 1/73. See also: Al-Tawdhih, explanation of the introduction of Abu al-Layth 94/b, and Bada'i' al-Sana'i 1/18, and Al-Ikhtiyar 1/48, and God knows best.