It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) prescribed a tenth ('ushr) on the produce of rain-fed land and land watered by rivers, and half a tenth (a twentieth) on produce irrigated by drawing water with buckets.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13053