We ask Almighty Allah, by His beautiful names and sublime attributes, to heal you from this problem. It should be noted that this is a kind of psychological disease that is known as Obsessive Compulsive Disorder, which refers to thoughts that dominate a person in some ways and persist with him even though he knows that they are mistaken and are not correct. This may be dealt with in several ways:
1 – Thinking positively of Allah, making a great deal of du’a (supplication), and beseeching Allah to heal you from this waswaas (insinuating whispers from Shaytan).
2 – Getting used to ignoring these waswaas and not paying any attention to them. You can put a suitable amount of water in a vessel, and do not make wudoo directly from the tap anymore; make yourself do wudoo from this vessel only. Tell yourself that there is no other water available except what is in this vessel, and make do with what it contains. Do not wash any part of the body more than three times. Even if the Shaytan tells you that your wudoo is not valid, this is just a whisper from the Shaytan and does not mean anything.
3 – The same applies to brushing your clothes after sitting in a place where someone else has sat. You should ignore this waswaas and force yourself not to brush your clothes. You should train yourself in this manner no matter what the waswaas is.
4 – You should remember the fiqhi (jurispudencial) principle which is that what is certain cannot be altered by something doubtful. If you are certain of something, you should not pay attention to any doubts after that. If you have done something then do not pay attention to any doubts that come along after doing it. If you have washed your hand, then do not pay any attention to doubts that come, even fleeting doubts, suggesting that you have not washed your hand, as Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
Doubts after doing something do not matter, otherwise doubts will increase.
You should not pay any attention to doubts that come after completing an act of worship, and even if a man has a lot of doubts he should not pay any attention to them.
5 – There is nothing wrong with consulting a trustworthy psychiatrist who can prescribe some useful treatment for you.
For more information please read Ighaathat al-Lahfaan by Ibn al-Qayyim and Talbees Iblees by Ibn al-Jawzi, which both discuss how the Shaytan toys with people by means of waswaas, and how one may remedy that.
We ask Allah to set your affairs and those of all the Muslims straight.