It was narrated from Abu Sa'eed Al-Khudri that:
The Prophet was asked about the water basins located between Makkah and Al-Madinah, which were visited by wild animals, dogs and donkeys, and about using them for means of purification. He said: "Whatever they (the animals) have carried in their bellies is for them, and whatever is left over is for us, and is pure." (DE)
English reference (DE): Vol. 1, Book 1, Hadith 519 (DE)
Arabic reference (DE): Book 1, Hadith 561 (DE)