Back when I was learning Daf Yomi, I ran into an interesting lesson I'm finding difficult to find again. It was a teaching that one should learn halacha from your rebbe's teachings and not through the observation of pious people. The reason, as I recall, was that the observation can be misleading. Observing the tzaddik may not take into account that he is properly relying on a heter, or perhaps that he is relying on a chumra. Therefore, one should only learn the halacha from the lectures. I can recall this lesson vividly, but I can't remember where I learned it. I thought it might be in Moed Kattan, but I haven't found it there in my review. Can anyone help? I need the source for an article I'm working on. Thanks.