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, and it was said that Ibn Jamil, Khalid bin al-Walid and Abbas (may Allah be pleased with them) had not given zakah. The Messenger of Allah (peace and blessings be upon him) said: "Ibn Jamil resents nothing except that he was poor and Allah made him rich. As for Khalid, you are wronging him; he has dedicated his armour and his equipment in the path of Allah. As for Abbas, his zakah is upon me, and as much again with it." Then he said: "O Umar! Do you not know that a man's uncle is like his father?"
In the narration of Shu'ayb bin Abi Hamzah from Abu al-Zinad it says: "then it is a charity due from him, and as much again with it." Ibn Ishaq and Abu Uways al-Madani from Abu al-Zinad, and Ibn Abi al-Zinad from his father, narrated: "it is due from him, and as much again with it." They understood this to mean that he (peace and blessings be upon him) had deferred the zakah for Sayyiduna Abbas (may Allah be pleased with him) for two years because of a need he had, while the narration of Warqa' means that he had taken two years' zakah from him in advance; and in this is evidence that paying zakah in advance is permissible. As for what Shu'ayb bin Abi Hamzah narrated, it is unlikely to be preserved, because Sayyiduna Abbas (may Allah be pleased with him) was of the direct lineage of Banu Hashim, for whom zakah is forbidden; so how could the Messenger of Allah (peace and blessings be upon him) make the two years' zakah due from him a charity to him? Musa bin Uqbah narrated from Abu al-Zinad: "then it is for him, and as much again with it"; "for him" can be used in the sense of "due from him", so his narration is understood in line with the other narrations. It may also be that "it is due from him" means due from the Prophet (peace and blessings be upon him), so that it agrees with the narration of Warqa'. The narration of Warqa' is more worthy of being authentic, because it agrees with the earlier narrations that explicitly mention taking in advance and hastening. And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7368