What is the ruling on wearing an iron ring?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Muslim scholars held different opinions regarding the ruling on wearing an iron ring. Some of them deemed it forbidden because of the Hadeeth indicating that a man came to the Prophet, sallallaahu ‘alayhi wa sallam, wearing an iron ring. The Prophet, sallallaahu ‘alayhi wa sallam, said to him: "Why is it that I see you wearing the jewelry of the inhabitants of Hellfire?" [Abu Daawood]

Imaam An-Nawawi commented on the Hadeeth of Sahl As-Sa‘idi where it is mentioned that the Prophet, sallallaahu ‘alayhi wa sallam, said to him: "Look for something (to present as a dowry), even if it be an iron ring." He said:

The Hadeeth underlines the permissibility of wearing an iron ring. Early scholars held different opinions in this regard, as stated by Al-Qadhi ‘Iyadh . The Shaafi‘i scholars held two views in this regard. The correct view is that it is not disliked to wear an iron ring because the Hadeeth suggesting the prohibition is weak. [Sharh Saheeh Muslim]

Hence, the questioner comes to know that this issue is controversial among the scholars. However, the preponderant opinion is that it is permissible because the Hadeeth on the prohibition of wearing an iron ring is weak.

Abu Al-Waleed Al-Baji said:

Abu ‘Umar said that the hadith that suggests the prohibition is not Muttasil (having a continuous chain of narrators).  Meanwhile,  things are permissible in principle, unless proven otherwise by virtue of authentic evidence. [Al-Muntaqa] 

Allaah Knows best.