Is the ablution valid for someone who performed it using previously used water out of ignorance of its ruling, such as one who washes a limb with water from the limb that preceded it?

According to many scholars, used water is sufficient for ablution so long as it has not changed. Therefore, it is permissible for one who adopts this view to have valid ablution and prayer. However, it is preferable to avoid it and perform ablution with other water.