If someone is uncertain whether their trousers are impure due to a possible splash of urine or just water, should they wash them and repeat their prayers, or is the doubt sufficient to consider them clean?
The doubt in impurity itself does not mean that the item is impure unless and until you have certain knowledge or concrete evidence that it is impure. You don't need to repeat your prayer just because of the doubt. If you want to repeat that prayer out of precaution, you can do so but it is not obligatory.
Wassalam.