The Kitāb al-āthar represents the lecture notes of two students of a single teacher who is alleged by the two students to be al-Shaybāni. These two attempted to write down in a verbatim fashion the traditions quoted by the teacher; however, when the teacher compared his views with those of other jurists, the students (or, at least, one of them) felt free to write down the comparisons in their own, personal styles. This discrepancy, I argue, confirms that the teacher was not a scholar who projected his own views back onto al-Shaybāni. The teacher was indeed al-Shaybāni himself. Stylistic analysis indicates that the book did not grow organically. It also shows that the Muwatta' of al-Shaybāni shared its origin with the Athār ; thus, the former, too, is authentic. The essay concludes with a comment on the authenticity of the materials attributed by al-Shaybāni to certain earlier authorities.