Sunan Ibn Majah 517
سنن ابن ماجه#517SahihIt was narrated from 'Ubaidullah bin 'Abdullah bin 'Umar that his father said:"I heard the Messenger of Allah being asked about water in the wilderness that is frequented by beasts and predators. The Messenger of Allah said: "If the water reaches the amount of two Qullah, nothing can make it impure (Najis).'" (Sahih) Another chain with similar wording
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Zubair Ali ZaiSahih
In-book reference: 1:251