How can one differentiate between obsessive whispers (waswasah) and other matters related to worship and purity, in order to disregard satanic whispers?

Occasional doubt in worship or purity is not considered an obsessive whisper (waswas). However, frequent doubts turn it into an obsessive whisper that should not be heeded. The one afflicted by waswas is he who frequently doubts in worship, and Maliki jurists refer to him as "one who is overtaken by doubt." Ibn Uthaymeen said: "The doubt of one afflicted by waswas is of no consequence, and for this reason the poet said: 'And doubt after an act has no effect and similarly if doubts become frequent.'"