Musnad Abu Ya'la al-Mawsili 153:176

Abu Khaythama narrated to us, from Muhammad ibn Ishaq, from Muhammad ibn Ja'far ibn al-Zubayr, from Ubayd Allah ibn Abd Allah ibn Umar, from Ibn Umar, who said: I heard the Messenger of Allah (peace be upon him) being asked about water that is in the open wilderness and what comes to it of beasts and predatory animals. The Prophet (peace be upon him) said: "When the water is the measure of two qullas, it does not carry impurity."