Leviticus 10:2
1 Then Aaron’s sons, Nadab and Abihu, each took his fire pan and put fire in it, set incense on it, and presented strange fire before the Lord, which he had not commanded them to do. 2 So fire went out from the presence of the Lord and consumed them so that they died before the Lord. 3 Moses then said to Aaron, “This is what the Lord spoke: ‘Among the ones close to me I will show myself holy, and in the presence of all the people I will be honored.’” So Aaron kept silent. 4 Moses then called to Mishael and Elzaphan, the sons of Uzziel, Aaron’s uncle, and said to them, “Come near, carry your brothers from the front of the sanctuary to a place outside the camp.”
Philo On Dreams 2.67
(2.67) But Moses will not allow the sacred reasonings about Nadab to be bewailed; for they have not been carried off by a savage beast, but have been taken up by unextinguishable violence and imperishable light; because, having discarded all fear and hesitation, they had duly consecrated the fervent and fiery zeal, consuming the flesh, and very easily and vehemently excited towards piety, which is unconnected with creation, but is akin to God, not going up to the altar by the regular steps, for that was forbidden by law, but proceeding rapidly onwards with a favorable gale, and being conducted up even to the threshold of heaven, becoming dissolved into ethereal beams like a whole burnt-offering.
Notes and References
"... What was the sin of Nadab and Abihu? The Bible says that they had brought an 'unholy' or 'foreign' fire before God. What exactly was wrong with this offering is not specified, nor did God's words cited immediately afterward - 'I will be sanctified among those who are close to Me, and before all the people I will be glorified' (Leviticus 10:3) - seem to clarify matters much ... All this notwithstanding, some interpreters claimed that no sin had been committed, and that Nadab and Abihu's death was actually a form of exaltation. After all, God's words in Leviticus 10:3 seemed to refer to Nadab and Abihu as 'those who are close to Me' (in the Septuagint, 'who draw near to Me'), and this sounded like a virtue, not a fault. What is more, the two were said to have died 'before the Lord' (Leviticus 10:2); did not this phrase seem to imply that they had not actually died in the tabernacle, but had ascended to heaven and died there? ..."
Kugel, James L. The Bible as it Was (pp. 441-442) Harvard University Press, 1998