One of the Quran verses on peace of mind

ٱلَّذِینَ ءَامَنُوا۟ وَتَطۡمَىِٕنُّ قُلُوبُهُم بِذِكۡرِ ٱللَّهِۗ أَلَا بِذِكۡرِ ٱللَّهِ تَطۡمَىِٕنُّ ٱلۡقُلُوبُ

- "Those who have believed and whose hearts are assured by the remembrance of Allah. Unquestionably, by the remembrance of Allah hearts are assured." (Surah Ar-Ra'd 13:28) 

This verse tells us that the source of peace and tranquility for our hearts and minds is the remembrance of Allah, which includes reciting His names, praising Him, glorifying Him, thanking Him, praying to Him, and reading His words. The more we remember Allah, the more we feel His presence, His mercy, His guidance, and His love in our lives. The more we remember Allah, the more we trust Him, rely on Him, and submit to Him in all situations. The more we remember Allah, the more we are protected from the whispers of Satan, the temptations of the world, and the worries of the future.