Musar for Sanhedrin 47:7
איני והאמר עולא הרואה את ר"ל בבית המדרש כאילו עוקר הרים וטוחנן זה בזה
The above text reads: 'Resh Lakish said: "Imagine a holy mouth [sc. R. Meir]uttering such a thing!" Read therefore [in the Mishnah], "The witness"[singular].' Surely this is not so! For 'Ulla said: One who saw Resh Lakishin the Beth-Hamidrash [engaged in debate] would think that he was uprootingmountains and grinding them against eachother!<span class="x" onmousemove="('comment',' So ingenious a mind did he have. How then could he be so modest as to refer to R. Meir as 'a holy mouth', thus implying that the latter's learning and skill was far above his own? — 'Mountain' is used figuratively for the problems overcome by dialectical ingenuity. ');"><sup>6</sup></span>