Musnad Ahmad 33:396

Zayd ibn al-Hubab narrated to us, 'Ayyash ibn 'Uqbah narrated to us, Khayr ibn Nu'aym narrated to me, from Abu al-Zubayr, from Jabir, from the Prophet, peace and blessings of Allah be upon him, who said: "Indeed, the ten are the ten of al-Adha, the witr (odd) is the day of 'Arafah, and the shaf' (even) is the day of the sacrifice."