Abu Sa'id al-Khudri said that God's messenger was asked about the purity of the cisterns between Mecca and Medina to which beasts of prey, dogs and asses go down, and replied, “They have what they carry in their bellies, and we have what is left as pure water.”
Abu Huraira reported God’s messenger as saying, “When a dog drinks out of a vessel belonging to any of you, he must wash it seven times,”
(Bukhari and Muslim) In a version by Muslim he said, “When a dog laps the water in a vessel belonging to any of you, he must wash it seven times, using earth the first time.”
Yahya b. Abd ar-Rahman said that ‘Umar went out with a party of riders among whom was ‘Amr b al-‘As. When they came to a cistern and ‘Amr asked its owner whether beasts of prey came down to it, ‘Umar said, “Don't tell us, owner of the cistern, for we go down to what beasts of prey leave, and they go down to what we leave.”
Malik transmitted it and Razin made an addition saying that some transmitters add to ‘Umar’s words that he said he had heard God’s messenger say, “They have in their bellies what they have taken, and what remains is pure for us and drinkable.”
