What is the ruling on a repentant person, formerly a transgressor, narrating Hadith?

Allah Almighty commanded verification and ascertainment when receiving news from a transgressor (fasiq), so it is not permissible to believe him merely based on his report, for he might lie, nor to disbelieve him before knowing his falsehood, for he might be truthful. Indeed, a transgressor might be truthful in his reports, especially if his transgression is not related to lying but to other aspects, such as a belief or opinion; he might even strive for truthfulness. However, if his transgression is due to lying and it is frequent and repeated, then his news and testimony are not accepted. If the transgressor repents and signs of his repentance appear, then his news is accepted, unless there is another impediment such as poor memory. The criterion is the state of the narrator at the time of reporting.