Hadith 639
´Abu Hurairah narrated that :` the Messenger of Allah said: "For what is watered by the heavens and steams, the Ushr is due, and for what is watered by irrigation, half of the Ushr."
Hadith 640
´Salim narrated from his father that :` the Messenger of Allah instituted the Ushr of what was watered by the heavens and steams, or through natural channels, and half of the Ushr for what is watered by irrigation.