It is a condition for the indication of the text in His saying: (And your garments purify); and from Ibn Umar, may Allah be pleased with them: ((The Messenger of Allah, peace be upon him, prohibited praying in seven places: in the garbage dump, the slaughterhouse, the graveyard, the roadside, in the bathhouse, in the places where camels kneel, and on the roof of the House of Allah)), in Sunan al-Tirmidhi 2: 177, and Sunan Ibn Majah 1: 246, and Musnad al-Ruyani 4: 126, and Sharh Ma'ani al-Athar 1: 384, and the prohibition was due to the assumption of impurity, which indicates the obligation of purification. See: Nafi' al-Mufti p. 225, and Jam' al-Rumuz 1: 80, and al-Maraqiy p. 208.