What is the ruling on the prayer of one who prayed with food remnants on his leg that he had walked on? And is it obligatory to repeat past prayers? And is it considered disbelief to deny that which is not deniable? And what is the ruling on not enjoining good and forbidding evil? And is the intention for prayer invalidated by忘记? And does ablution become void by unintentionally touching used water?

Food is a blessing that must be thanked and not demeaned. Trampling on it is intensely disliked (makrooh). Any food particles clinging to the foot must be removed before ablution (wudu) or ritual bath (ghusl (definition)) so as not to prevent water from reaching the skin. However, if food particles adhere after ablution, the prayer (salat) is valid. Denying something that is not an evil due to ignorance, or not denouncing an evil, does not constitute disbelief (kufr). One should not proceed to denounce something until it is known to be an evil, for among the conditions of enjoining good and forbidding evil is knowledge of both.