Q: What is the size of the impurity that is overlooked in Shariah, i.e. the amount that can be left unwashed and your prayer will still be valid?
A. The soiled portion should not be more than the size of the hollow of the palm, which is about 16cm in diameter. If this line of impurity is equal to 16cm or more, it will not be excusable. Less than this will be excusable.
Allah Ta’aala knows best.
Mufti Siraj Desai