Sayyiduna Abu Umamah al-Bahili (may Allah be pleased with him) narrates from Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him), from the Messenger of Allah (peace and blessings be upon him), that he said: "Allah, the Mighty and Majestic, has given you as charity one third of your wealth at the time of your death, as an increase to (the deeds of) your life, so that it may become a means of purification for you in your deeds."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17230