Why did Ismāʿīl b. ʿUlayyah reject the charge of backbiting against “not thabt”?

The Necessity and Boundaries of Narrator Criticism

• The criticism was valid, but backbiting only occurs outside the gathering
• It was a relevant critical judgment on precision, not personal disparagement
• He judged chain continuity, not the narrator’s precision
• Ismāʿīl approved it because the criticism was made in a private gathering