A reliable narrator must possess two broad qualities: ʿadālah (probity) and ḍabṭ (precision). Probity concerns honesty, religious and ethical conduct, and factors bearing on trust. Precision concerns receiving, retaining, and accurately conveying a report.
Five causes chiefly concern probity: lying, accusation of lying, immoral conduct, unknown status, and doctrinal innovation. Five chiefly concern precision: excessive error, carelessness, hidden mistake, contradiction of reliable transmitters, and weak memory.
These are analytic categories, not impermeable compartments. Repeated serious errors or anomalies may cast grave doubt on accuracy, whereas deliberate lying strikes at the narrator's basic honesty.