Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) sent Sayyiduna Umar (may Allah be pleased with him) to collect zakah.
Sayyiduna Abu Humayd al-Sa'idi (may Allah be pleased with him) said: He (peace and blessings be upon him) appointed a man called Ibn al-Lutbiyyah as collector over the zakah of Banu Sulaym. When he came back, he took account from him. There are other hadiths on this as well.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7358
Ibn Shihab (may Allah have mercy on him) narrates that Abu Bakr and Umar (may Allah be pleased with them both) did not take zakah doubled (two years at once); rather, they sent collectors for it in drought and in plenty, in times of fatness and of leanness, because the beloved Prophet (peace and blessings be upon him) collected zakah every year. Therefore this is the Sunnah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7359