It is narrated from Sayyiduna Abu Sa'id (may Allah be pleased with him): We were with the Messenger of Allah (peace and blessings be upon him). We came to a pool in which there was a carcass. Some of the people performed ablution and some held back until the Prophet (peace and blessings be upon him) would come. The Prophet (peace and blessings be upon him) came at the rear of the people and said: "Perform ablution and drink, for nothing makes water impure."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1218