Does the prayer of a person afflicted with urinary incontinence become invalid if he considers what has come out to be mere whisperings and does not change his clothes?

The waswas (whispers/obsessive thoughts) have reached a significant level with you, and the only cure for them is to ignore them and pay them no heed. Do not concern yourself with these waswas, and whenever they present themselves to you, cast them away. Do not investigate whether anything has exited or not, and do not change your clothes. You are not held accountable for what is in reality, but you are obligated by the rulings of Sharia based on what is apparent. If you turn away from doubt and waswas and something truly exited from you without your knowledge, you are not held accountable for it due to your lack of knowledge of the true state of affairs. The default is that which is not doubted. So, whoever doubts whether something has exited from him should not pay attention to this doubt until he is certain, as in the hadith: "He should not leave until he hears a sound or perceives a smell." We reiterate our advice to you to ignore these waswas and pay them no attention, no matter what Satan casts into your heart, for he is not concerned with your well-being; rather, his goal is to distance you from Allah.