Imam As Sa’di (Rahimahullah) in explanation of this verse:
“And this is also from the mannerisms that are upon those of understanding to adorn themselves with and use. And that is if a sinful individual informs them of some news/information, that they verify that news/information from him and don’t just simply accept it. For indeed in that is great danger and (vulnerability) of falling into sin. For his relaying of news, if it is made the same as the relaying of news by the truthful reliable person, a person judges and rules based on that news and what it necessitates. And so resulting from this, the loss of life and wealth without due right owing to that news and information, that which results in regret.
Rather, that which is obligatory at the point of receiving some news from the sinful person is to verify and clarify. And if the proofs and supporting factors point towards his truthfulness, it is to be acted upon and believed in, and if they point towards him lying, it is not believed in nor acted upon.
So in this is a proof that the news from the truthful is accepted, the news from the liar is rejected and the news from the sinful individual is to be held back from (accepting or rejecting it) as we mentioned. That is why the Salaf would accept the narrations from many of the Khawarij, those who were well-known for their truthfulness, although they were sinful.”
Tayseer Al Kareem Ar Rahmaan of Imam Sa’di