It is narrated from Sayyiduna Anas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) wore a ring whose engraving was 'Muhammad Rasulullah' (Muhammad is the Messenger of Allah) (peace and blessings be upon him); whenever he (peace and blessings be upon him) went to the toilet, he would take it off.
This is a weak supporting narration (shahid).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 451