Midrash sa Levitico 4:15: Sifra & Vayikra Rabbah

1) (Vayikra 4:15): "And the elders of the congregation (shall place their hands upon the head of the bullock"): I might think old people from the marketplace; it is, therefore, written: "the elders of the congregation" (i.e., beth-din). If "the elders of the congregation," I might think all the elders in the congregation (i.e., even the beth-din of twenty-three); it is, therefore, written "the congregation," the distinctive of the congregation (i.e., the Great Sanhedrin).

2) And how many (elders) are they? "And they shall place" — two; "elders" — two; beth-din cannot be equi-balanced (a condition which might result in a judicial stalemate) — (one is added), all together, five. These are the words of R. Yehudah. R. Shimon says: "And the elders shall place" — two; beth-din cannot be equi-balanced — (one is added), all together, three.

3) "their hands" — the (two) hands of each one. "upon the head of the bullock": The bullock requires semichah, but the idolatry goats do not require semichah. These are the words of R. Yehudah. R. Shimon says: The bullock requires semichah by the elders; the idolatry goats do not require semichah by the elders, (but by the Cohein). For R. Shimon says: Every communal sin-offering whose blood enters within (to be sprinkled on the golden altar) requires semichah.