Obligatory Charity Tax (Zakat)

Bukhari :: Book 2 :: Volume 24 :: Hadith 560

Narrated Salim bin 'Abdullah from his father:

The Prophet said, "On a land irrigated by rain water or by natural water channels or if the land is wet due to a near by water channel Ushr (i.e. one-tenth) is compulsory (as Zakat); and on the land irrigated by the well, half of an Ushr (i.e. one-twentieth) is compulsory (as Zakat on the yield of the land)."