Sahih Muslim Book 22, Hadith Number 4838.

Chapter : Of what age the animal is to be sacrificed.

Uqba b. ‘Amir reported that Allah’s Messenger (may peace be upon him) gave the gifts of goats to be distributed amongst his Companions. They sacrificed them, but a lamb of one year of age was left. (Someone) made a mention of that to the Messenger of Allah (may peace be upon him), whereupon he said: You sacrifice it.