Sahih Bukhari, Chapter: Obligatory Charity Tax (Zakat)

Allah's Apostle said, "If one give in charity what equals one date-fruit fro the honestly-earned money and Allah accepts only the honestly earned money --Allah takes it in His right (hand) ar then enlarges its reward for that person (who has given it), as anyone of you brings up his baby horse, so much so that it becomes as big as a mountain.