Musnad Ahmad 1018:62

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from ‘Asim ibn Kulayb, from his father, from a man from Muzaynah or Juhaynah, who said: When it was a day or two before the Adha, the companions of the Prophet, may Allah bless him and grant him peace, would give a *jadha‘ah* (a lamb at least six months old) and take a *thaniyyah* (a sheep at least one year old). The Messenger of Allah, may Allah bless him and grant him peace, said: "The *jadha‘ah* suffices for that which the *thaniyyah* suffices."