He used to wear his ring like this, placing its stone on the back of his hand. The narrator said, "I do not think Ibn Abbas mentioned this except that he was reporting that the Messenger of Allah ﷺ used to wear his ring in this manner."
حدثنا عبد الله بن سعيد حدثنا يونس بن بكير عن محمد بن إسحق قال رأيت على الصلت بن عبد الله بن نوفل بن عبد المطلب خاتما في خنصره اليمنى فقلت ما هذا
يلبس خاتمه هكذا وجعل فصه على ظهرها قال ولا يخال ابن عباس إلا قد كان يذكر أن رسول الله ﷺ كان يلبس خاتمه كذلك
Its chain is hasan. Tirmidhi narrated it in the chapter on clothing, in the section on wearing the ring on the right hand, hadith no. 1742, from the hadith of Muhammad bin Ishaq, and Bukhari graded it hasan.