Quran 13:28 from Surah Ar-Ra'd on Divine Marvels.
ٱلَّذِينَ ءَامَنُواْ وَتَطۡمَئِنُّ قُلُوبُهُم بِذِكۡرِ ٱللَّهِۗ أَلَا بِذِكۡرِ ٱللَّهِ تَطۡمَئِنُّ ٱلۡقُلُوبُ
English translation: Those who believed and find satisfaction their hearts in the remembrance (of) Allah No doubt in the remembrance (of) Allah find satisfaction the hearts
Transliteration: alladhina amanu watatma-innu qulubuhum bidhik'ri al-lahi ala bidhik'ri al-lahi tatma-innu al-qulubu