Musnad Abu Ya'la al-Mawsili 3:21

Narrated to us Zuhayr, narrated to us Abd al-Rahman, from Sufyan, from Asim ibn Kulayb, from Abu Burdah, from Ali, who said: The Messenger of Allah (may Allah bless him and grant him peace) forbade me from placing the ring in this or in this—the index finger and the middle finger.