Mukhtasar Muslim

It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) that he heard the Noble Prophet (peace and blessings of Allah be upon him) say: In the (field) which is irrigated by canals and rain, ‘ushr (i.e., one-tenth) is obligatory as zakat, and in that which is irrigated by camels (i.e., by manual labor), nisf al-ushr (i.e., one-twentieth) is obligatory as zakat.