Mishnah, Pe'ah 2:6

Rabbi Shimon of Mizpah once sowed his field in the presence of Rabban Gamliel. They then went up to the chamber of hewn stones [in the temple, where the Sanhedrin met] and asked [whether a field sown with two types of wheat requires that two corners of the field be left for the poor, or only one.] Nachum, the scribe, said "I have [the answer] from Rabbi Miasha, who heard from his father, who heard from the pairs [of early sages], who heard from the prophets that it is the law going back to moses at Sinai regarding one who sows his field with two types of wheat: if he reaps the entire field at one time, then he leaves one corner; if he reaps at two times, then he must leave two corners." [translation by Rabbi Daniel S. Nevins]