Al-Fath 48:4

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.

He (Allah) is such that He sent down tranquility into the hearts of the believers, so that they grow more in faith in addition to their (existing) faith- And to Allah belong the forces of the heavens and the earth, and Allah is All-Knowing, All-Wise-