The Messenger of Allah (ﷺ) said: "When the amount of water reaches the equivalent of two large pitchers, it does not accept impurity." In this hadith, there is an explanation of the pitchers of the place called Hajar. Ibn Jurayj said: "I have seen the pitchers of the place Hajar; one pitcher is equal to two leather water-skins or two and a little more of water."
Hadith Referenceمسند الإمام الشافعي / كتاب الطهارة / 5
Hadith Takhrijإسناده ضعيف؛ لضعف مسلم بن خالد الزنجي ولجهالة من حدث عنه ابن جريح. أخرجه عبدالرزاق: (2)، (259)، والدارقطني: 1/ 24.