Abu Ubayd (may Allah have mercy on him) said: I was present at Eid with Sayyiduna Umar bin al-Khattab (may Allah be pleased with him), and he began with the prayer before the sermon. Then he said that the Messenger of Allah (peace and blessings be upon him) "forbade fasting on these two days: as for the Day of Adha, on it you eat from your sacrifices; and as for the Day of Fitr, it is the day of breaking your fasts."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8249