2 verses have
“serenity”
in Edition Clear Qur'an by Talal Itani / Al-Fath (The Victory)
48:18God was pleased with the believers, when they pledged allegiance to you under the tree. He knew what was in their hearts, and sent down serenity upon them, and rewarded them with an imminent conquest.
48:26Those who disbelieved filled their hearts with rage—the rage of the days of ignorance. But God sent His serenity down upon His Messenger, and upon the believers, and imposed on them the words of righteousness—of which they were most worthy and deserving. God is aware of everything.
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Those who spend their wealth by night and day, privately and publicly, will receive their reward from their Lord. They have nothing to fear, nor shall they grieve.
The Holy Quran · Al-Baqara (The Cow) · 2:274