Tafsir of Az-Zumar 39:33-35

{And he who has brought the truth and believed in it} He is the Messenger of Allah (ﷺ). He brought the truth and believed in it. He intended by this [singular pronoun] himself and those who followed him, just as He intended by [the mention of] Moses himself and his people in His saying: {And We certainly gave Moses the Scripture that perhaps they would be guided} (Al-Mu'minun: 49). Therefore, He said: {Those are the righteous}, except that this is in terms of the attribute, while that was in terms of the name.

It is also permissible that it refers to the group or party that brought the truth and believed in it; they are the Messenger who brought us the truth and his companions who believed in it. In the reading of Ibn Mas‘ud, it is: {And those who brought the truth and believed in it}.

It has been read: {wa-ṣadaqa bihi} (with a light dal), meaning: the people believed him regarding it and did not call him a liar concerning it. It means: he delivered it to them exactly as it was revealed to him, without distortion. It is also said: he became ṣādiqan (truthful) by it—meaning because of it—because the Qur’an is a miracle, and a miracle is a verification from the Wise One (who does not do what is ugly) for the one upon whose hands it is performed. It is not permissible for Him to verify anyone except the truthful one; thus, he becomes, by virtue of the miracle, truthful. It has also been read: {wa-ṣaddaqa bihi}.

If you ask: What is the meaning of attributing "the worst" and "the best" to what they did, and what is the meaning of the superlative form in both?

I say: As for the attribution, it is not the attribution of the superlative (af‘al) to the group over which it is preferred; rather, it is the attribution of a thing to that which is a part of it without preference, like your saying: "Al-Ashaj is the most just of the Banu Marwan."

As for the preference, it is an indication that the bad deed which might occur from them—from the minor sins and slips that are expiated—is, in their view, "the worst" due to their magnification of disobedience. And the good deed they perform is, in the sight of Allah, "the best" due to the excellence of their sincerity in it. Therefore, He mentioned their bad as "the worst" and their good as "the best." It has also been read: {aswā’u} (plural of sū’).

{Is Allah not sufficient for His servant? And they threaten you with those other than Him. And whoever Allah leaves astray - for him there is no guide. And whoever Allah guides - for him there is no misleader. Is Allah not Exalted in Might, Owner of Retribution?}