Musnad Abu Ya'la al-Mawsili 3:153

Ubayd Allah ibn Umar narrated to us, Hammad ibn Zayd narrated to us, Ayyub narrated to us, from Nafi, from Ibrahim ibn Hunayn, from Ali, who said: The Messenger of Allah (may Allah bless him and grant him peace) forbade me from reciting [the Quran] while I am bowing (ruku), and from wearing silk-blend garments (al-qassi), and [from wearing] a gold ring.