Surah Ar-Ra'd, ayah 28

ٱلَّذِينَ ءَامَنُواْ وَتَطۡمَئِنُّ قُلُوبُهُم بِذِكۡرِ ٱللَّهِۗ أَلَا بِذِكۡرِ ٱللَّهِ تَطۡمَئِنُّ ٱلۡقُلُوبُ ٢٨

Alladhīna āmanū watatma'innu qulūbuhum bidhikrillāhi alā bidhikrillāhi tatma'innul-qulūb

Those who have believed and whose hearts are assured by the remembrance of Allāh. Unquestionably, by the remembrance of Allāh hearts are assured."