I say, and with God's success: It is what exceeds the amount of a dirham - which is the weight of a dirham, and it is a mithqal in density, and the area of the dirham is about the width of the palm in lightness, and the width of the palm is the concave width of the palm, which is within the joints of the fingers - as for the amount of the dirham and what is less than it, it is excused; because the little is excused by consensus, and it is measured by the dirham; because the place of istinja is measured by it, and they found it distasteful to mention the buttocks in their gatherings, so they referred to it as the dirham; and because necessity includes the buttocks and others, it is excused for hardship, and it is thick due to the lack of opposition to the evidence of its impurity: like blood and similar things where there is no conflict of texts. See: Al-Wiqayah and its explanation by Sadr al-Shari'ah, p. 132, and Kanz al-Daqaiq 1: 73, and God knows best.