Musnad Ahmad 33:551

Hassan narrated to us, Ibn Lahi'ah narrated to us, from Abu al-Zubayr, from Jabir, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "In what is watered by the sky (rain) and springs, there is a tenth. And in what is watered by the water-drawing camel (irrigation), there is half a tenth."