Narrated Anas:
The Prophet got a ring made for himself and said, "I have got a ring made (for myself) and engraved a certain engraving on it so none of you should get such an engraving on his ring." I saw the glitter...
Glory is to You, O Allah, and praise; I bear witness that there is none worthy of worship but You. I seek Your forgiveness and turn to You in repentance.
Info: An-Nasa'i, 'Amalul-Yawm wal-Laylah, p. 173. See also Al-Albani, 'Irwa'ul-Ghalil 1/135 and 2/94.