It is narrated from Ibn Abbas (may Allah be pleased with them both) that when the Messenger of Allah (peace be upon him) sent Muadh bin Jabal (may Allah be pleased with him) to (Yemen), he said to him: "If they accept this, then inform them that there is charity (zakat) due upon them, which is to be taken from their wealthy and returned to their needy."
Hadith Referenceمسند الإمام الشافعي / كتاب الزكاة / 673
Hadith Takhrijاخرجه البخارى الزكاة، باب أخذ الصدقة من الاغنياء وترد في الفقراء حيث كانوا (1496) ومسلم، الإيمان، باب الدعاء الى الشهادتين وشرائع الاسلام (19)۔