Musnad Ahmad 31:814

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, who said: Sulayt ibn Ayyub ibn al-Hakam al-Ansari narrated to me, from 'Ubayd Allah ibn 'Abd al-Rahman ibn Rafi' al-Ansari, then one of the Banu 'Adi ibn al-Najjar, from Abu Sa'id al-Khudri, who said: It was said to the Messenger of Allah, peace and blessings of Allah be upon him: "O Messenger of Allah, how can water be drawn for you from Bi'r Bida'ah, the well of Banu Sa'idah, when it is a well into which the menstrual rags of women, the flesh of dogs, and the filth of people are thrown?" The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, water is purifying; nothing makes it impure."