I once heard a reference to a story in the gemara about an amora who is saying a shiur and a certain person in the bais medrash calls the amora a ganiv (thief) because he can't follow the shiur so he quotes the pasuk "torah tzivah lanu moshe, morashah kehillas yaakov".
Is there such a story in the Gemara and if so, where?
I think you are referring to the following from Sanhedrin 91b (translation artscroll)
אמר רב יהודה אמר רב כל המונע הלכה מפי תלמיד כאילו גוזלו מנחלת אבותיו
שנאמר (דברים לג, ד) תורה צוה לנו משה מורשה קהילת יעקב
Rav Yehudah said in the name of Rav: Whoever withholds the teaching of the law from the mouth of a student (i.e., whoever neglects to teach Torah to a student) is as if he robs [the student] of his ancestral heritage. For it is stated The Torah that Moses commanded us is the heritage of the congration of Jacob.