Sahih Muslim Book 6, Hadith Number 2534.
Chapter : Forbiddance to observe fast on ‘Id-ul-Fitr and ‘Id-al-Adha.
Abu Huraira (Allah be pleased with him) reported that the Messenger of Allah (may peace be upon him) forbade to observe fast on these two days. ‘Id-ul-Adha bi and ‘Id-ul-Fitr.