All Praise is due to Allah Alone and peace and blessings be upon His Messenger, his family, and Companions.
Istinja' or Istijmar (cleansing the private parts with hard material after urination or defecation) is a must after passing urine or stool. Without it, the Wudu' and Salah are invalid. (Part No. 5; Page No. 104) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.