In another narration: «The one who buys a muhaffala and returns it, let him return a ssaa’ with it.» It was only named muhaffala because the milk was subject to tahfeel and accumulated in its udder. Everything that you increase, you would have performed tahfeel to it. It is from it that it was said: «The people assembled » if they gather and increase. It was for this that an assembly of the people was named, and the plural of an assembly is assemblies .