﴿ ٱلَّذِينَ ءَامَنُوا۟ وَتَطْمَئِنُّ قُلُوبُهُم بِذِكْرِ ٱللَّهِ ۗ أَلَا بِذِكْرِ ٱللَّهِ تَطْمَئِنُّ ٱلْقُلُوبُ ﴾

“those who believe, and whose hearts find their rest in the remembrance of God - for, verily, in the remembrance of God [men's] hearts do find their rest-:”

Please check ayah 13:29 for complete tafsir.