This phrase is part of a famous saying by Rabbi Chanina, found in the Talmud (Ta'anit 7a): "הרבה למדתי מרבותי, ומחבירי יותר מהם, ומתלמידי יותר מכולם." This means: "I have learned much from my teachers, more from my colleagues, but from my students more than all of them." The saying highlights the profound idea that teaching others and interacting with students can be a powerful source of learning and growth for the teacher.