The Yalkut Shimoni (27:776) says:
The Gemara (AZ 18a) brings that Rav Chanina ben Tradion was wont to publicly gather numerous students to teach them Torah, at a time when doing so was a capital crime. When caught and sentenced to be burned together with his Sefer Torah, he asked Rav Yossi ben Kisma, "Am I worthy to merit Olam Habba?" Rav Yosi responded, "כלום מעשה בא לידך", have you ever done anything extraordinary? Rav Chanina answered that one time he inadvertantly commingled his own money and money he was entrusted for the poor on Purim, and he gave all the money to the poor, afraid to calculate how much was his. Rav Yosi said "אם כן מחלקך יהי חלקי ומגורלך יהי גורלי", if so, may I share your portion, may I share your lot.
Odd, that Rav Chanina's mesiras nefesh didn't rate as highly as his decision to avoid even a vanishingly small risk of taking a penny from the poor. Why was Rav Yossi so impressed? And consider that Rav Yossi ben Kisma, who was so amazed, is the one that said (Avos 6:9)
See also the Gemara (Chagiga 9b)
Without being over on Lo Sechaneim, let me say that someone else once put it very nicely, as follows:
“Faithfulness in great things is not uncommon; faithfulness in little things is rare but most indicative of character. Almost any husband would leap into the sea or rush into a burning building to rescue his perishing wife. But to anticipate the convenience or happiness of the wife in some small matter, the neglect of which would go unnoticed, is a more eloquent proof of tenderness.
“Our lives for the most part are made up of little things, and by these our character is to be tested. There are very few who have to take a prominent place in the great conflicts of our age; the vast majority must dwell in humbler scenes and be content to do a more humble work. The conflicts which we have to endure either against evil in our own soul or in the moral circle where our influence would seem to be trivial are in reality the struggle of the battle for life and decency; and true heroism is shown here as well as in those grander scales in which others win the leader’s fame or the martyr’s crown. Little duties carefully discharged; little temptations earnestly resisted with the strength which God supplies... these all together help to form that character which is to be described not as popular or glamorous, but as moral and noble.”
I think it's important to note that to the extent that I understand Rav Dessler's interpretation of the story of Rav Yossi and Rav Chanina ben Dosa, I don't agree with his pshat. The great men that I knew lived minutely and meticulously examined lives, and Rav Chanina's concern about the Purim money certainly would have merited careful thought and a conscious decision even if he personally thought money was dirt. I remember hearing from Reb Moshe that he paskens hundreds of shailos a day on his own behavior. The Medrash that he brings does support his idea, though, because it involves things that are truly insignificant- how you treat sheep. In any case, it goes without saying that Rav Dessler's point is true and important in regard to our own life experience.)