Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) says that he (peace and blessings be upon him) was asked: "O Messenger of Allah! May we perform ablution from the well of Buda'ah, when it is a well into which foul things, carcasses, menstrual cloths and (dead) dogs are thrown?" He (peace and blessings be upon him) said: "Water is pure; nothing makes it impure."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1214