What is the ruling when impurity is in the flowing water (less than two qullahs) that meets a two-qullah body of still water?
Chapter on what purification is achieved with regarding water
Al-Mughni
Book of Purification
Primary text
If the impurity is in the flowing river, and the river is two qullahs, it remains pure. If the river is less than two qullahs, it is impure prior to meeting the still water. Upon meeting the still water, it becomes pure through connection. If they separate, the river portion reverts to impurity due to its small volume while containing impurity.
Supporting text
It is also suggested that the flowing water remains pure upon meeting the still water because it is a large volume of water that has not changed; therefore, it does not become impure, based on the prophetic statement: 'When water reaches two qullahs, nothing pollutes it.' This latter view is the position of Al-Shafi'i.