Ubaidullah bin 'Abdullah bin 'Umar عبيد الله بن عبد الله بن عمر بن الخطاب · The Book on Purification

"I heard AlIah's Messenger while he was being asked about water in open areas of the land, and predators and beasts come to it." He said: 'So Allah's Messenger said: 'When the water is two Qullah it does not carry filth.'"