What is the ruling on obsessive thoughts (waswasah) concerning purification and prayer, and what should be done about them? Is washing with water after urination correct? And what is the ruling on previous prayers that were performed without knowledge of the obligation to wash the male organ?

The cure for obsessive thoughts is to disregard them and not pay them any attention. So, if Satan whispers to you that your prayer is invalid, do not pay attention to his whispers. Wiping the private parts with water is not sufficient for istinja' (cleaning oneself after relieving oneself); rather, it is necessary to pour water on the place of impurity until it is highly probable that the impurity has been removed. As for missed prayers, many scholars hold that they must be made up, while some do not, such as Sheikh Al-Islam Ibn Taymiyyah, who believes that whoever omits a condition out of ignorance is not required to repeat it. The Hanafis do not consider istinja' obligatory in the first place. If you are afflicted with obsessive thoughts, there is no harm in not making up these prayers, acting upon the opinion of those who do not oblige you to repeat them.