All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If you doubt that your shirt is stained with blood or other impurities, then the ruling is that your shirt remains pure and it is not ruled to be impure just by doubting about its impurity as in principle it is pure and there is doubt about its impurity, and certainty cannot be removed by doubt as we clarified in Fatwa 92050.
The same thing applies to anything else that is pure and you doubt about its impurity but you are not certain that it is impure, so it remains pure and it is not ruled to be impure.
Based on that, you should not take into consideration this doubt and your shirt is pure and you can pray in it. So, you should not open the door to obsessive whispers.
Allaah Knows best.