Musannaf Ibn Abi Shayba 35:44

Abu Usama narrated to us, from al-Walid ibn Kathir, from Muhammad ibn Ka'b, from Ubayd Allah ibn Abd Allah, from Rafi' ibn Khadij, from Abu Sa'id al-Khudri: It was said, "O Messenger of Allah, shall we perform ablution from Bi'r Bida'ah, while it is a well into which menstrual cloths, the flesh of dogs, and filth are thrown?" The Prophet, may Allah bless him and grant him peace, said, "Water is purifying; nothing makes it impure."