Imam al-Shafi'i (may Allah have mercy on him) says: The hadith of the well of Buda'ah, in which it is stated that the well of Buda'ah had a great deal of deep water, and filth used to be thrown into it which did not change its colour or taste, nor did any foul smell appear in it. It was said to the Prophet (peace and blessings be upon him): You perform ablution from the well of Buda'ah although such and such things are thrown into it? The Prophet (peace and blessings be upon him) said in reply: "Nothing makes water impure." From this it became clear that this applied to water in the same condition as that about which he (peace and blessings be upon him) gave the answer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1260