Musar for Sanhedrin 171:2
מאי קושיא דילמא הא ר"ש הא רבנן
Read [instead], 'He is exempt.' But what difficulty is this: perhaps the latter is R. Simeon's view [only]. and the former the Rabbis'? — You cannot think so, for R. Johanan said: [The author of] an anonymous Mishnah is R. Meir; of an anonymous Tosefta, N. Nehemiah; of an anonymous [dictum in the] Sifra, R. Judah; in the Sifre, R. Simeon;<span class="x" onmousemove="('comment',' Rabbi (R. Judah ha-Nassi), in compiling the Mishnah, drew upon earlier collections, of which each Tanna possessed one. An anonymous Mishnah is based upon R. Meir's collection, though not necessarily reflecting R. Meir's views. For this interpretation. v. Weiss, Dor. Vol. II, pp. 51f; Strack, Introduction to Talmud and Midrash, p. 21, The Tosefta, as its name implies ('addition') is a further elaboration and development of Tannaitic teaching, closely allied to the Mishnah. The relation of the Mishnah to the Tosefta is a problem which has so far remained unsolved; v. Strack, op. cit., pp. 74ff. The Sifra (also called [H]) is the traditional interpretation of Leviticus, to which is prefaced an exposition of the Thirteen Principles of Hermeneutics of the School of R. Ishmael. Though ascribed here to R. Judah b. Ila'i, our version contains many additions by later teachers, and its final compilation is generally assigned to R. Hiyya. It is also occasionally referred to as the Sifra debe Rab (of the College of Rab). Whether this is to indicate Rab's authorship is one of the literary problems, among others, which the Sifra presents. (V. Weiss, op. cit pp. 193 seqq.) The Sifre contains the commentary on Num. V to the end of Deut. This too contains additions later than R. Simeon, to whom it is here ascribed, and is a composite work shaped by the School of Rab (v. Weiss, op. cit.), but in any case the Sifre now extant is not identical with the Talmudic Sifre. ');"><sup>2</sup></span>