In the text referenced as "Avot deRabbi Natan, Version B 13. As cited in Noam Zion, "Can Later Rabbinic Creativity Transcend its Origins: Moshe v. Akiva in the Talmud," Shalom Hartman Institute, June 1, 2008.
(ג) אמר לו, אמשול לך משל למה הדבר דומה, למעין זה שהוא נובע ומוציא מים, ויש בכוחו להוציא מים יותר ממה שהוא מכניס. כך אתה יכל לומר דברי תורה יותר ממה שקבלו מסיני. אמר לו, שמא ממני אתה מתבייש, הריני עומד מאצלך. עמד רבן יוחנן והלך לו לחוץ, והיה רבי אליעזר יושב ודורש ופניו מאירות כאור החמה, וקרנותיו יוצאות כקרנותיו של משה, ואין אדם יודע אם יום ואם לילה. בא רבן יוחנן מאחוריו ונשקו על ראשו. אמר לו, אשריכם אברהם יצחק ויעקב שיצא זה מחלציכם.
(3) (R. Jochanan) said to him, I will (also) tell thee a parable. To what is the matter like? To this fountain which is bubbling and sending forth its water, and it is able to effect a discharge more powerful || than what it secretes; in like manner art thou able to speak words of the Torah in excess of what Moses received at Sinai. (R. Jochanan) continued: Lest thou shouldst feel ashamed on my account, behold I will arise and go away from thee. Rabban Jochanan ben Ẓakkai arose and went outside. (Thereupon) R. Eliezer sat down and expounded. His face shone like the light of the sun and his effulgence beamed forth like that of Moses, so that no one knew whether it was day or night. They went and said to Rabban Jochanan ben Ẓakkai: Come and see R. Eliezer sitting and expounding, his face shining like the light of the sun and his effulgence beaming like that of Moses, so that no one knows whether it be day or night. He came from (his place) behind him and kissed him on his head, saying to him: Happy are ye, Abraham, Isaac, and Jacob, because this one has come forth from your loins.