The World Federation One Stop Fiqh

Ruling 685

If a person forgetfully or neglectfully performs tayammum with a usurped thing, his tayammum is valid. However, if that thing has been usurped by him and he forgets that he has usurped it, then considering his tayammum as being valid is problematic [i.e. based on obligatory precaution, his tayammum must not be considered to be valid].