Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) narrates that the Messenger of Allah (peace and blessings be upon him) said: On crops irrigated by rivers and springs, one-tenth (ushr) is obligatory as zakat, and on crops irrigated by waterwheels (wells), half of one-tenth (one-twentieth) is obligatory.
Hadith Referenceالمنتقى ابن الجارود / كتاب الزكاة / 347
Hadith Gradingغلام مصطفےٰ ظهير امن پوري:صحيح
Hadith Takhrijاز غلام مصطفےٰ ظهير امن پوري:«صحيح مسلم : 981»