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.”
Ibn Majah transmitted it.
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…