Musnad Ahmad 31:784

Ahmad ibn Abd al-Malik narrated to us, Sharik narrated to us, from Ibn Abi Layla, from Amr ibn Murrah, from Abu al-Bakhtari, from Abu Sa’id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The *wasq* is sixty *sa’s*."