Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "When you have paid the zakah, you have fulfilled what is obligatory upon you. And whoever gathers unlawful wealth and then gives it in charity will have no reward for it; rather, its burden will fall upon him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7240