Sunan Ibn Majah, Chapter: The Chapters of Purification and its Sunnah

that the Prophet (saw) 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." (Daif)