Allah says in Surah ar-Ra'd:

''Those who believe, and whose hearts find comfort in the remembrance of Allah. Surely, it is in the remembrance of Allah that hearts find comfort.” (Verse 28)

Yes, in the remembrance of Allah those who believe will find rest in their hearts. Because that these souls feel their constant attachment to Allah. Because these souls know that everything in the world is from Allah. They know that anybody can do nothing but Allah. They know that the happiness of this world and of next world belongs to Allah. So then why should the hearts not find rest in the remembrance of Allah?

‘’Surely, it is in the remembrance of Allah that hearts find comfort.”

Only those who have tasted it will know what is the resting. The unbelievers are totally unaware of what the resting of the heart is. They are the most miserable people on earth. The happiest people in the world are those who turn to Allah, those who are guided, those who believe and whose hearts find rest in the remembrance of Allah.