Reward of teaching others Torah:
Teach others and Hashem will teach you: Chazal state that one who teaches others Torah, on him the verse states “Meir Eiyneiy Shneiyhem”, that Hashem enlightens both of their eyes. This means to say that when one who is rich in Torah knowledge teaches another who is poor in Torah knowledge, then Hashem who is rich in Torah knowledge will teach the teacher, who also has areas of Torah knowledge in which he needs enlightenment. Hashem shines upon both the student and teacher His Divine countenance.
Will teach him in future: Whoever teaches one Torah in this world will merit to teach Torah also in the world to come.
 Temura 16a, brought in Tanya Hakdama
 Temurah ibid
 Based on Rashi ibid
 Tanya Hakdama
 Rav Sheshes in Sanhedrin 92a