What is the recommended manner of using stones for comprehensive cleansing?
Chapter on Cleaning oneself (Istitabah) and Impurity (Hadath)
Al-Mughni
Book of Purification
Primary text
It is recommended that the first stone cleanses the right side surface from front to back, then moves to the left surface, returning to the starting point. The second stone should then be used similarly on the left surface. The third stone should be used on the posterior exit point (masraba) and both surfaces. This is based on the Prophet's saying: "Does not one of you find two stones for the two surfaces and one stone for the masraba?" It is necessary that each stone covers the entire area, as partial application constitutes compounding, resembling a single wipe rather than repetition.
Supporting text
A potential alternative interpretation is that it suffices to wipe each area once, based on the apparent meaning of the report.