Sunan an-Nasai Book 23, Hadith 2490

أَخْبَرَنَا هَنَّادُ بْنُ السَّرِيِّ، عَنْ أَبِي بَكْرٍ، - وَهُوَ ابْنُ عَيَّاشٍ - عَنْ عَاصِمٍ، عَنْ أَبِي وَائِلٍ، عَنْ مُعَاذٍ، قَالَ بَعَثَنِي رَسُولُ اللَّهِ صلى الله عليه وسلم إِلَى الْيَمَنِ فَأَمَرَنِي أَنْ آخُذَ مِمَّا سَقَتِ السَّمَاءُ الْعُشْرَ وَفِيمَا سُقِيَ بِالدَّوَالِي نِصْفَ الْعُشْرِ ‏.‏

It was narrated that Mu'adh said:"The Messenger of Allah sent me to Yemen and he commanded me to take one-tenth of whatever is irrigated by the sky, and half of one-tenth of whatever is irrigated by means of buckets