What's the difference between the Muslim and the Mumin?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Islam means total obedience and submission to Allah, observance of His Orders and avoidance of His Prohibitions; bringing one's likes and dislikes into harmony with the Divine Will.

As for Eaman, it is related to the heart. It is the belief of the heart in Allah that He is the Lord of the worlds and no one deserves to be worshipped except Him.

The Prophet said: "Islam (means what a Muslim acts) in public and Eaman is (what one believes) in the heart." [Ahmad from Anas Ibn Maalik, may Allah be pleased with him]

Shaykh Shaakir, while commenting on the book of at-Taahawiyyah creed, said: “This Hadeeth has authentic narration.”

Thus, a person has to know that there is no true Eaman without Islam, and vice versa. In other words, belief without action is of no use, nor is action without belief of any value.

At the same time, when Eaman or Islam is mentioned in the Quran or the Sunnah, each one means the other. Allah Says (what means): {Indeed, the religion in the sight of Allah is Islam.} [Quran 3:19] The verse includes both of Eaman (what is in the heart) and Islam (what is done openly).

The Prophet said: "Eaman consists of more than seventy branches, the best of which is the acknowledgement of the fact that "La Ilaaha Illa Allah" (None has the right to be worshipped but Allah), and the lowest of them is the removal of a thing causing harm from a thoroughfare." [Muslim]

Here, Eaman includes actions and beliefs. As a final word, we draw your attention to the following two points:

1) If you recognize the difference between Eaman and Islam, then the difference between the Muslim and Mu’min (believer) becomes clear.

2) Eaman increases with good deeds and decreases with evil deeds.

For more benefit, please refer to Fatwa 83219.

Allah knows best.