Tosefta for Sanhedrin 175:18
תנן כך דרשתי וכך דרשו חבירי כך למדתי וכך למדו חבירי מאי לאו דהוא אמר מפי השמועה והם אומרין כך הוא בעינינו לא הוא אומר כך הוא בעיני והם אומרים מפי השמועה
"'Within thy gates" — this refers to the gleanings, forgotten [sheaves] and the corner of the field'. 'The gleanings,' even as we learnt: Two ears [that fell down] are gleanings [to be left for the poor], three are not. As to forgotten sheaves — two [forgotten] sheaves are [treated as] 'forgotten' [i.e., must be left for the poor]; three are not. And concerning all these Beth Shammai ruled: Three belong to the poor, four to the landowner.<span class="x" onmousemove="('comment',' Hence, if three fell down, and embroiled the rebellious elder and the Beth Din in a dispute, the question of ownership involves the validity of kiddushin, as explained on p. 579, n. 3. ');"><sup>18</sup></span>