Musnad Abu Ya'la al-Mawsili 7:23

Musa ibn Muhammad ibn Hayyan narrated to us, Muhammad ibn Umar ibn Abdullah al-Rumi narrated to me, he said: I heard al-Khalil ibn Murrah narrating from Mubashir, from al-Zuhri, from Abu Salamah ibn Abd al-Rahman ibn Awf, from his father, from the Prophet, peace be upon him, who said: "The superiority of the scholar over the worshiper is seventy degrees; between each two degrees is like what is between the heaven and the earth."