Though Islam makes purification a condition of the validity of salah, a Muslim is encouraged not to fall a prey to Satanic whisperings regarding purification.
Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: “As a muslim, while praying: if you are suffering from incontinence, or bladder control problems, then you should do the following:
You should make sure to wash yourself and perform ablution immediately before the salah you intend to perform. After having done so, if, during the course of your salah, you were to experience any wetness, drops, etc., you need not worry about it as it shall be considered as “excused” in your case. Allah, the Almighty tells us clearly: “He has not appointed any hardship for you in your religion.” (Al-Hajj: 78) But once again, we must stress that in this case, one must only perform the necessary purification and wudu’ as close to the time of the salah as possible.
Regarding the second scenario: If you do not suffer from incontinence or bladder control problems, then you must ask yourself whether you are certain that you have started your salah after having performed the necessary purification and wudu’ or not. If you are certain that you have done so, then you need not pay any attention to such intrusive thoughts or doubts that might assail your mind unless you see some definite signs indicating otherwise. Such signs include wetness, a foul smell or the sound of passing wind, etc. If you were to experience any of these signs, you must break your salah and only resume it after having performed the requisite procedure of purification and wudu’.
If, on the other hand, you did not experience any such definite signs that have been indicated above, then you do not need to pay any attention to these thoughts. This is in accordance with the principle of Fiqh that, “Certainty cannot be undermined by mere doubt or hesitation.” Therefore, you should continue your salah until such time that you see clear signs to the contrary.
In the case indicated above, it is important for us to know that such nagging doubts are due to the whisperings of Satan, as the Prophet (peace and blessings be upon him) told us that Satan will approach us in our salah, trying to distract us from performing it properly. In doing so, he will definitely try different ways with different people. If, in your case, he is trying to cast doubts in your mind regarding your purification, with someone else he may suggest some other troublesome thoughts, and, hence, the remedy for it is simply turning to Allah for protection and invoking His help against the accursed one.”