A teacher must recognize the limits of his knowledge and retention. If he is uncertain about wording or isnād, pausing, checking an original copy or stating the uncertainty is scholarly integrity.
An unverified recollection should not be transmitted confidently as though it were established. Teacherly dignity lies in accurate disclosure, not an immediate answer to every question.
Students should be able to hear the wording clearly, ask needed questions and record it accurately. Nevertheless, the responsibility for completing and verifying one's own hearing also belongs to the student.