The World Federation One Stop Fiqh

Ruling 271

If a person forgets that some water is usurped and performs wuḍūʾ with it, his wuḍūʾ is valid. However, if someone usurps some water himself and then having forgotten that it is usurped performs wuḍūʾ with it, then to consider his wuḍūʾ as being valid is problematic [i.e. based on obligatory precaution, it must not be considered to be valid].