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."  

قَالَ رَسُولُ اللَّهِ ﷺ فِيمَا سَقَتِ السَّمَاءُ وَالْعُيُونُ الْعُشْرُ وَفِيمَا سُقِيَ بِالنَّضْحِ نِصْفُ الْعُشْرِ قَالَ وَفِي الْبَابِ عَنْ أَنَسِ بْنِ مَالِكٍ وَابْنِ عُمَرَ وَجَابِرٍ  

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