The first is the category of the great rivers that Allah Most High has caused to flow and that human beings did not dig, such as the Tigris and the Euphrates. Their water is abundant enough for irrigation and drinking, and no shortage could reasonably be imagined, nor is there any need for dispute or contention over it. Thus, anyone may take irrigation water from them for his estate and make a drainage outlet from his estate into them. No one may prevent him either from taking irrigation water or from making such a drainage outlet.

The second category is the small rivers caused to flow by Allah. These are of two types. The first is one whose water rises even without being held back and suffices all those who use it without any shortfall. Every landowner among them may take water to irrigate his land when he needs it, and they are not to obstruct one another. If some people wish to draw a channel from it to convey water to another land, or to make the drainage outlet of another river flow into it, the matter must be examined. If this would harm the people who use this river, it is prohibited; but if it would not harm them, it is not prohibited.

The second type is one whose water is limited and does not rise sufficiently for irrigation unless it is held back. The first of those who use the river begins by irrigating his land until he has taken enough and it is saturated. Then the person next downstream holds it back, and so on until the last of them, whose land is the last in the sequence of those holding it back. Each person may retain enough water on his land to reach the ankles. When it reaches that level, he releases it to the next person. Aḥmad expressly stated this in the narration of Abū Ṭālib, saying: “As for flowing water, it is held back for the people of the upper reaches to the depth of the ankle,” and he cited the hadith.

The wording of the hadith is that which Abū Bakr narrated through his chain of transmission from Thaʿlaba ibn Abī Mālik al-Quraẓī, who said: “The Messenger of Allah (Allah bless him and grant him peace) ruled concerning Mahzūr, the valley of Banū Qurayẓa, that the water should be held to the ankles, with the upstream party holding it back for the downstream party.” Through his chain of transmission from ʿAmr ibn Shuʿayb, from his father, from his grandfather, he also narrated that the Messenger of Allah (Allah bless him and grant him peace) “ruled concerning the floodwater of Mahzūr that it be held back until it reached the ankles, then the upstream party was to release it to the downstream party.”