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.
عَنْ رَسُولِ اللَّهِ ﷺ أَنَّهُ سَنَّ فِيمَا سَقَتِ السَّمَاءُ وَالْعُيُونُ أَوْ كَانَ عَثَرِيًّا الْعُشْرُ وَفِيمَا سُقِيَ بِالنَّضْحِ نِصْفُ الْعُشْرِ