Sayyiduna Ali (may Allah be pleased with him) said: Sayyiduna Abbas (may Allah be pleased with him) asked the Messenger of Allah (peace and blessings be upon him) about paying his zakah early, before it became due, and he (peace and blessings be upon him) gave him permission.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7365