Sayyiduna Anas bin Malik (may Allah be pleased with him) said that a man from Banu Tamim came to the Messenger of Allah (peace and blessings be upon him) and said: O Messenger of Allah! When I have given the zakah to your envoy, am I then free of it before Allah and His Messenger? The Messenger of Allah (peace and blessings be upon him) said: "Yes, when you have paid it to my envoy, you are free of it. Its reward is yours, and its sin is upon the one who altered it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7283