What is the ruling on actions that stem from one afflicted by obsessive-compulsive disorder (waswasah) concerning their ablution (wudu), prayer (salat), creed ('aqeedah), and cleanliness, and what afflicts them of the waswasah of disbelief (kufr), and related rulings?

There is no cure for obsessive thoughts except to ignore and dismiss them, coupled with the certainty that a Muslim does not exit Islam merely because of such thoughts. Do not renew your Islam nor repent from disbelief due to the whispers of Satan. Whoever commits what necessitates disbelief out of ignorance, error, or misinterpretation is excused. A person does not disbelieve until their heart is opened to disbelief. Read the Qur'an normally and strive to understand its meanings, seek refuge in Allah from Satan, do not be annoyed by repentance, and do not imagine that your words are disbelief. You may also consult a trusted doctor.