(Al-Fajr) 89 : 27
يَا أَيَّتُهَا النَّفْسُ الْمُطْمَئِنَّةُ
Oh, the soul who has attained tranquillity.
As explained in verses 13: 28 and 15: 99, peace and tranquillity of the heart, as well as confirmed belief that one is destined for Paradise, can only be achieved with Adhikr — the Confirming Truth. See explanation 12: 53 and 75: 2.