Pirkei Avot §avot_02_08: Rabban Yohanan ben Zakkai received [the oral tradition] from Hillel and Shammai.

Rabban Yohanan ben Zakkai received [the oral tradition] from Hillel and Shammai. He used to say: if you have learned much Torah, do not claim credit for yourself, because for such a purpose were you created. Rabban Yohanan ben Zakkai had five disciples and they were these: Rabbi Eliezer ben Hyrcanus, Rabbi Joshua ben Hananiah, Rabbi Yose, the priest, Rabbi Shimon ben Nethaneel and Rabbi Eleazar ben Arach. He [Rabbi Johanan] used to list their outstanding virtues: Rabbi Eliezer ben Hyrcanus is a plastered cistern which loses not a drop; Rabbi Joshua ben Hananiah happy is the woman that gave birth to him; Rabbi Yose, the priest, is a pious man; Rabbi Simeon ben Nethaneel is one that fears sin, And Rabbi Eleazar ben Arach is like a spring that [ever] gathers force. He [Rabbi Yohanan] used to say: if all the sages of Israel were on one scale of the balance and Rabbi Eliezer ben Hyrcanus on the other scale, he would outweigh them all. Abba Shaul said in his name: if all the sages of Israel were on one scale of the balance, and Rabbi Eliezer ben Hyrcanus also with them, and Rabbi Eleazar ben Arach on the other scale, he would outweigh them all.