It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) as a marfu' report that the Messenger of Allah (peace and blessings be upon him) said: "A Muslim man does good with a third (of his wealth) at the time of his death, and Allah thereby completes his zakah."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10422