What is the ruling on one who suffers from obsessive-compulsive whispers (waswas) concerning purity, prayer, and creed? And does a person become a disbeliever if these whispers afflict him?

The cure for obsessive thoughts is to disregard them and not pay attention to them. Your dislike and aversion to them are a sign of the sincerity of your faith. Strive against these obsessive thoughts and repel them from yourself, and seek refuge with Allah from Satan. As for obsessive thoughts related to purity and prayer, do not pay attention to them and do not repeat anything from your prayers, ablution, or ritual bath.