Rabbi Isser Zalman Meltzer was talking to a student who quoted the Pri Megadim, a commentary on the Shulchan Oruch.
- based on Twerski's Visions of the Fathers pg. 391
When he heard the quote, Rabbi Isser Zalman exclaimed, "The Pri Megadim did not say that!"
The student reached for the book where he thought he saw the quote, but Rabbi Isser Zalman stopped him. "Let us first see whether it is possible for the Pri Megadim to have said that," and proceeded to explain the Pri Megadim's method of analysis, showing how this particular statement would be inconsistent with that approach.
Sure enough, the statement did not appear in the Pri Megadim's commentary.
"Do not think that I know the Pri Megadim by heart," Rabbi Isser Zalman said, "However, knowing the approach a Torah scholar has in Torah enables one to know what kind of statements he may have made."