What is the ruling on wiping small drops of urine from the legs with a wet tissue, and what must one do concerning the prayers performed in this state?

It is not sufficient to merely wipe away urine drops with a tissue, even if they are small; rather, it is necessary to wash them with water. This is because purification from impurity is a condition for the validity of prayer, and whoever prays while knowingly carrying an impurity, their prayer is invalid and they must repeat it. This applies whether the urine is abundant or scarce, provided it is possible to guard against it.

Scholars have explicitly stated the obligation to wash any part of the body or clothing affected by urine, and wiping is not sufficient. The proof for this is the Prophet's (peace and blessings of Allah be upon him) saying: "Cleanse yourselves from urine, for indeed, the general torment of the grave is because of it."

However, if you were doing this out of ignorance, then you are not required to repeat the prayers that were performed in that state.