Which hand:?
- It is recommended to wear rings on the right hand. It is stated that wearing the ring on the right hand is from the signs of a believer.
- Wearing rings on the left hand is disliked (makruh).

Which stones are recommended:
The following stones are recommended for rings:
1. Aqeeq (عقيق - Agate/Carnelian)
2. Firuzaj (فيروزج - Turquoise)
3. Chinese Iron (الحديد الصيني)

Source References:

The following passages from Sayed Sistani's rulings support this answer:

Question 2: "Is it true that wearing rings on the left is disliked?"
Answer: "Wearing the ring on the right hand is from the signs of a believer." (من علامات المؤمن التختّم باليمين)

Question 3: "What are the stones that are recommended for rings?"
Answer: "Aqeeq, turquoise, and Chinese iron." (العقيق والفيروزج والحديد الصيني)

Source: https://www.sistani.org/arabic/qa/0667/

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Which Finger and which hand

Shaikh  Hilli Video https://youtu.be/DwyUsUrj0Wk

Allowed Hands for Ring Wearing

• It is encouraged to wear rings on the right hand, as it is considered mustahabb (recommended).
• The left hand is permissible for ring-wearing, though historical context suggests a cautionary view due to past associations.
• There are no explicit narrations prohibiting wearing rings on the left hand, but it is advised to wear rings on both hands, prioritizing the right.

Recommended Fingers for Ring Placement

• Rings should primarily be worn on the small finger and the ring finger.
• Wearing rings on other fingers, such as the thumb or middle finger, is generally discouraged and not well-established in tradition.
• Excessive ring-wearing, especially on all fingers, is not in line with traditional practices.

Cultural and Spiritual Considerations

• Wearing too many rings can lead to concerns about vanity and distract from spiritual focus.
• Some individuals may place excessive importance on rings, potentially leading to beliefs that stray towards polytheism.
• It is emphasized that while rings can symbolize blessings, ultimate reliance should be on Allah rather than the items themselves.

It is recommended to wear rings on the right hand, specifically on the little finger and the ring finger. If you choose to wear any rings on the left hand, you should ensure that you have at least one ring on the right hand and preferably on the little finger of the right hand.
It is not recommended to wear rings on the other fingers.