Although Islam makes purification a condition of the validity of salah, a Muslim is encouraged not to fall a prey to Satanic whisperings regarding purification. One must be certain of the act that nullifies one’s ablution. Ibn Al-Mubarak said: “If one is uncertain about one’s condition of purity, one does not need to perform a new ablution.” Further, if one is certain that his ablution has been nullified and doubts whether he has purified himself or not, he must perform a new ablution.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
“The Prophet (peace and blessings be upon him) said, “If during of the course of Prayer one doubts whether his wudu’ is broken or not, he needs not leave the place (to renew wudu’) unless he senses some foul smell or hears the sound (of passing gas).” Likewise, if you are in doubt about discharge of urine, you need not leave the salah unless you feel the wetness. If after the completion of salah, you feel the wetness in your underwear or body, then you ought to renew your wudu’ and repeat your salah.
however, if you are suffering from incontinence, then you certainly fall in the category of those who are allowed special dispensations because of your specific condition. In this case, what is required of you is to wash yourself and perform your wudu’ as closely as possible to the salah you are about to perform. Once you have done so you need not worry about what happens after. Your salah is considered as perfectly valid because of your specific health condition. For Allah says, (Allah does not wish to impose on any soul such burdens that it has no strength to bear) (Al-Baqarah 2: 285).”