Musnad Abu Ya'la al-Mawsili 42:255

Zuhayr narrated to us, Wahb ibn Jarir narrated to us, my father narrated to me, he said: I heard Yunus narrating from al-Zuhri, from Abu Salamah ibn Abd al-Rahman, from Abu Sa’id al-Khudri, from the Prophet (peace and blessings of Allah be upon him), who said: "There was no prophet sent, nor was there a successor appointed, except that he had two inner circles (bitanatan): an inner circle that commands him to do good and urges him toward it, and an inner circle that commands him to do evil and urges him toward it. And the protected one is he whom Allah protects."