3 verses have
truthful
in Edition Clear Qur'an by Talal Itani / An-Naml (The Ant)

27:49They said, “Swear by God to one another that we will attack him and his family by night, and then tell his guardian, 'We did not witness the murder of his family, and we are being truthful.'“

27:64Or, who originates the creation and then repeats it, and who gives you livelihood from the sky and the earth? Is there another god with God? Say, “Produce your evidence, if you are truthful.”

27:71And they say, “When is this promise, if you are truthful?”