Al-Fath 48:4
هُوَ ٱلَّذِىٓ أَنزَلَ ٱلسَّكِينَةَ فِى قُلُوبِ ٱلْمُؤْمِنِينَ لِيَزْدَادُوٓا۟ إِيمَـٰنًا مَّعَ إِيمَـٰنِهِمْ ۗ وَلِلَّهِ جُنُودُ ٱلسَّمَـٰوَٰتِ وَٱلْأَرْضِ ۚ وَكَانَ ٱللَّهُ عَلِيمًا حَكِيمًا
Huwa allathee anzala assakeenatafee quloobi almu/mineena liyazdadoo eemanan maAAaeemanihim walillahi junoodu assamawatiwal-ardi wakana Allahu AAaleeman hakeema
"It is He who sent down tranquility into the hearts of the believers that they would increase in faith along with their [present] faith. And to Allāh belong the soldiers of the heavens and the earth, and ever is Allāh Knowing and Wise."
Al-Fath 48:4, translation by Sahih International
A short reflection
It is He who sent down tranquillity into the hearts of the believers, that they may increase in faith with their faith.