Midrash for Pirkei Avot 2:8
רַבָּן יוֹחָנָן בֶּן זַכַּאי קִבֵּל מֵהִלֵּל וּמִשַּׁמָּאי. הוּא הָיָה אוֹמֵר, אִם לָמַדְתָּ תוֹרָה הַרְבֵּה, אַל תַּחֲזִיק טוֹבָה לְעַצְמְךָ, כִּי לְכָךְ נוֹצָרְתָּ. חֲמִשָּׁה תַלְמִידִים הָיוּ לוֹ לְרַבָּן יוֹחָנָן בֶּן זַכַּאי, וְאֵלּוּ הֵן, רַבִּי אֱלִיעֶזֶר בֶּן הוֹרְקְנוֹס, וְרַבִּי יְהוֹשֻׁעַ בֶּן חֲנַנְיָה, וְרַבִּי יוֹסֵי הַכֹּהֵן, וְרַבִּי שִׁמְעוֹן בֶּן נְתַנְאֵל, וְרַבִּי אֶלְעָזָר בֶּן עֲרָךְ. הוּא הָיָה מוֹנֶה שִׁבְחָן. רַבִּי אֱלִיעֶזֶר בֶּן הוֹרְקְנוֹס, בּוֹר סוּד שֶׁאֵינוֹ מְאַבֵּד טִפָּה. רַבִּי יְהוֹשֻׁעַ בֶּן חֲנַנְיָה, אַשְׁרֵי יוֹלַדְתּוֹ. רַבִּי יוֹסֵי הַכֹּהֵן, חָסִיד. רַבִּי שִׁמְעוֹן בֶּן נְתַנְאֵל, יְרֵא חֵטְא. וְרַבִּי אֶלְעָזָר בֶּן עֲרָךְ, מַעְיָן הַמִּתְגַּבֵּר. הוּא הָיָה אוֹמֵר, אִם יִהְיוּ כָל חַכְמֵי יִשְׂרָאֵל בְּכַף מֹאזְנַיִם, וֶאֱלִיעֶזֶר בֶּן הוֹרְקְנוֹס בְּכַף שְׁנִיָּה, מַכְרִיעַ אֶת כֻּלָּם. אַבָּא שָׁאוּל אוֹמֵר מִשְּׁמוֹ, אִם יִהְיוּ כָל חַכְמֵי יִשְׂרָאֵל בְּכַף מֹאזְנַיִם וְרַבִּי אֱלִיעֶזֶר בֶּן הוֹרְקְנוֹס אַף עִמָּהֶם, וְרַבִּי אֶלְעָזָר בֶּן עֲרָךְ בְּכַף שְׁנִיָּה, מַכְרִיעַ אֶת כֻּלָּם:
R. Yochanan ben Zakkai received it from Hillel and from Shammai. He was wont to say: If you have learned much Torah, do not take credit for it, [to say: "I have learned much Torah." For you were created for this. (It is because he left neither Scripture, Mishnah, halachah, and aggadah which he did not learn, that he said this.)] R. Yochanan ben Zakkai had five disciples: R. Eliezer ben Hurkanos, R. Yehoshua ben Chananiah, R. Yossi Hakohen, R. Shimon ben Nethanel, and R. Elazar ben Arach. He was wont to cite their (respective) distinctions: R. Eliezer ben Hurkanos — a lime-coated pit, that does not lose a drop. [So, he too does not lose one item of his learning]. R. Yehoshua — [He was so replete in good middoth that all said about him: "Happy is she who bore him!" (Others say: They said this because it was she who caused him to be a sage. She would make the rounds of all the houses of study in her city and say to them (the disciples): "Please, pray for this fetus in my stomach, that he be a sage!" And from the day that he was born, she did not remove his crib from the house of study, so that only words of Torah enter his ears.] R. Yossi — chasid, [acting above and beyond the letter of the law.] R. Shimon ben Nethanel — a fearer of sin, [stringent with himself and forbidding to himself permitted things out of fear that he might come to sin. For if not so, what is special about this? Even an ignoramus can be a fearer of sin.] R. Elazar ben Arach — a resurgent well, [of broad heart, "welling up" dialectic and conjecture of his own.] He (R. Yochanan ben Zakkai) was wont to say: If all the sages of Israel were in one balance of the scale and Eliezer ben Hurkanos in the other, he would outweigh them all. Abba Shaul says in his (R. Yochanan b. Zakkai's) name: If all the sages of Israel were in one balance of the scale and R. Eliezer ben Hurkanos also with them, and R. Elazar (ben Arach) in the other, he would outweigh them all. [I have found it written that Abba Shaul does not disagree with the first tanna and that both things were said by R. Yochanan ben Zakkai and both are true. In comprehensive knowledge and memory, R. Eliezer (ben Hurkanos) outweighed them all, and in sharpness and dialectic R. Elazar ben Arach outweighed them all.]