What is the difference between a doubt (shubah) in belief, and thinking about it and researching to dispel it, and doubt (shakk) in religion? Does a person disbelieve (kafara) due to doubts? Is it obligatory to seek refuge (from Satan), spit, and say "I believe in Allah and His messengers" with every whisper (waswas) or only when it persists and takes control? And is one sinful if they ignore a fleeting thought without applying that?

The treatment for creedal whisperings is to turn away from them, ignore them, and pay them no mind. If you have learned matters of creed and achieved faith, then do not pay attention to the whisperings of Satan. Whoever strives against whisperings is on the path of good. Seeking refuge [with Allah] when a whispering occurs is commendable but not obligatory, and there is no sin upon one who does not seek refuge; however, seeking refuge is more complete and preferable.