The fingers the Prophet forbade the men to wear the ring on!!

Most of the scholars of Hadith and Fiqh are of the opinion that it is Sunna and recommended for a male, if he chooses to wear a silver ring, to wear it on his little finger of the hand.

Imam Muslim (may Allah have mercy on him) reports in the chapter pertaining to clothing and adornment (Kitab al-Libas wa'l Zina) in his Sahih from Sayyiduna Anas ibn Malik (may Allah be pleased with him) that he said: "The ring of the Messenger of Allah (Allah bless him & give him peace) was on this", and he pointed towards the little finger of his left hand. (Sahih Muslim, no: 2095)

Sayyiduna Ali (may Allah be pleased with him) says: "The Messenger of Allah (Allah bless him & give him peace) forbade me that I wear a ring on this or this finger of mine." The narrator says that he pointed to the middle finger and the one next to it [i.e. the index finger]." (Sahih Muslim, no: 2078)

Based on the above narrations, the renowned Shafi'i jurist and Hadith scholar, Imam Nawawi (may Allah have mercy on him) states:

"Muslim scholars have agreed that it is a Sunna [for men] to wear the ring on the little finger. As for women, they may wear rings on their various fingers." (Al-Minhaj sharh Sahih Muslim, P: 1584)

Imam Nawawi (may Allah have mercy on him) then explains the reason for wearing the ring on the little finger. He says that the other fingers are more frequently used when utilizing the hand, whilst the little finger is not so frequently used due to it being at the corner of the hand. As such, he says, it is somewhat disliked (makruh tanzih) for a man to wear his silver ring on the middle and index fingers. (ibid)