What is the Shar'i definition of waswas, and what is the distinguishing line between genuine waswas and other types in the context of purification?

"Waswasah" (whispering of evil suggestions) is the self and Satan speaking about things that are of no benefit or good. It is not built upon a foundation, unlike doubt, which is hesitation between two equal possibilities and is built upon a foundation. The noble Hadith has pointed to Allah's favor, who turned Satan's plot into mere "waswasah."