Tafsir of Al-Ahzab 33:8

ليسٲل الصادقين عن صدقهم

That He may ask the truthful about their truth. Mujahid said: "This refers to, those who convey the Message from the Messengers.''

وأعد للكافرين

And He has prepared for the disbelievers. i.e., among their nations,

عذابا أليما

a painful torment. i.e., agonizing. We bear witness that the Messengers did indeed convey the Message of their Lord and advised their nations, and that they clearly showed them the truth in which there is no confusion, doubt or ambiguity, even though they were rejected by the ignorant, stubborn and rebellious wrongdoers. What the Messengers brought is the truth, and whoever opposes them is misguided. As the people of Paradise will say:

لقد جاءت رسل ربنا بالحق

Indeed, the Messengers of our Lord did come with the truth. (7:43)