Sahih Muslim Book 22, Hadith Number 4839.

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

Amir al-Juhani reported: Allah’s Messenger (may peace be upon him) distributed sacrificial animals (amongst us for sacrificing them on ‘Id al-Adha). So we sacrificed them. There fell to my lot a lamb of less than one year I said: Allah’s Messenger, there has fallen to my lot a lamb (Jadha’a), whereupon he said: Sacrifice that.