Musnad Ahmad 28:212

Waki’ narrated to us, Abdullah ibn Abd al-Rahman narrated to us, he heard it from Amr ibn Shu’ayb, from his father, from his grandfather: "That the Prophet, peace and blessings of Allah be upon him, performed twelve takbirs in the Eid prayer: seven in the first [rak'ah] and five in the last. And he did not pray before it, nor after it." [Abdullah ibn Ahmad said]: My father said: "And I hold this view."