3 verses have
“truthful”
in Edition Clear Qur'an by Talal Itani / Al-A'raaf (The Heights)
7:70They said, “Did you come to us to make us worship God alone, and abandon what our ancestors used to worship? Then bring us what you threaten us with, if you are truthful.”
7:106He said, “If you brought a miracle, then present it, if you are truthful.”
7:194Those you call upon besides God are servants like you. So call upon them, and let them answer you, if you are truthful.
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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