Abu Rafi' (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) granted Abu Rafi' a piece of land. When Abu Rafi' died, Umar (may Allah be pleased with him) sold it for eighty thousand and gave (the money) to Ali (may Allah be pleased with him), and he used to pay its zakah. When the sons of Abu Rafi' took possession of it, they found it less, so they came to Ali (may Allah be pleased with him) and informed him. Ali (may Allah be pleased with him) said: Did you calculate its zakah? They said: No. Then, when they calculated the zakah, they found it exactly complete. Ali (may Allah be pleased with him) said: Did you think that I would have wealth with me and not pay its zakah?
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7343