Yahya related to me from Malik from Muhammad ibn Yahya ibn Habbanfrom al-Araj from Abu Hurayra that the Messenger of Allah, may Allahbless him and grant him peace, forbade fasting on two days - the dayof the Id al-Fitr and the day of the Id al-Adha.
USC-MSA web (English) reference: Book 20, Hadith 137
Arabic reference: Book 20, Hadith 840