Guarded From Heaven

Rav Nosson never ate food that was cooked on Pesach itself. He ate only food that had been cooked before Yom Tov in his own special keilim. Before Pesach, any tiny amount of chametz that might have entered the food is nullified. But in food cooked on Pesach itself, not even a mashehu (a minute amount) of chametz is nullified, even one part in a thousand.

It is told that one year, after his Pesach food had been prepared and heated, someone unwittingly stirred it with a spoon that was not one of his special keilim. The entire dish then fell and shattered, and all the food was ruined. Later the mistake with the spoon was discovered, and people saw how Heaven had saved him from transgressing his own stringencies.

Similarly, someone once brought him wine to make Kiddush on Shabbos morning, and the bottle fell and broke and all the wine spilled. It was discovered afterward that the wine had not met his standards of kashrus.