Allah has condemned both the liar and the one who denies the truth, as He says in more than one verse:
“Who does greater wrong than one who fabricates a lie against Allah or denies the truth when it comes to him?”
[Surah al-Ankabūt: 68]
And He says:
“Who does greater wrong than one who fabricates a lie against Allah or denies His signs?”
[Surah al-Anām: 21]
Accordingly, among the qualities with which Allah described the prophets—who, of all people, are most worthy of this quality—is that each of them brings the truth and does not lie. Each is truthful himself and affirms others as truthful.
Since the phrase “And the one who” denotes a class rather than a particular individual being intended (1), He referred back to it with a plural pronoun, saying:
“And the one who brought the truth and affirmed it—those are the God-fearing.”
[Surah al-Zumar: 33]
You will find many of those who claim affiliation with knowledge and religion do not lie in what they say (2); indeed, they say nothing but the truth. Yet they do not accept the truth reported by others. Rather, caprice and ignorance lead them to brand others liars even when they are truthful—whether they are branding a peer a liar or branding (3) someone outside their faction.
The very act of calling a truthful person a liar is itself a lie. For this reason, He paired such a person with one who lies (4) against Allah, saying:
“Who does greater wrong than one who lies against Allah and denies the truth when it comes to him?”
[Surah al-Zumar: 32]
Thus, both are liars: [the former lies] (5) in what he reports about Allah, whereas the latter lies in what he says about the person who reports from Allah.