LEV19 One who renders a halachic decision in his Torah teacher's presence is punishable with misah [bidei Shamayim] ["death at the hands of Heaven" -- AJL]. Our Sages, z"l, said (Eruvin 63a) that the reason Nadav and Avihu died when offering up an unauthorized fire (See Vayikra 10:1-2) was not for the sin of the offering, since their intent was to perform a mitzvah; for they said, "The Torah states (Vayikra 1:7), 'The sons of Aharon the Kohen shall place fire on the mizbe'ach' -- although the fire descends from heaven, it is a mitzvah for man to bring it." (I.e., in this they interpreted the verse incorrectly, but their intentions were pure and this would not have normally been punished. This concurs with the opinion of Ra'avad, brought by Rashba and others, that Nadav and Avihu offered incense on the inner, golden mizbe'ach in an incorrect way. Their punishment, however, resulted from their rendering a halachic decision in the presence of Moshe Rabbeinu.