Should I repeat my prayer after performing Tayammum if it later became clear to me that I could have purchased water?

The prayer performed with tayammum must be repeated if water was available for purchase, because jurists hold that one is obligated to buy water if it is available at a reasonable price. For many jurists, forgetfulness does not waive the obligation of repetition, because it is a purification that is obligatory when one remembers, and the ability to purchase water means that the person is not truly lacking water.