Aaron's sons Nadab and Abihu each took his own firepan, put fire in it, placed incense on it, and presented unauthorized fire before the Lord, which He had not commanded them [to do].
References for Leviticus 10:1
Then flames leaped from the Lord's presence and burned them to death before the Lord.
References for Leviticus 10:2
So Moses said to Aaron, "This is what the Lord meant when He said: I will show My holiness to those who are near Me, and I will reveal My glory before all the people." But Aaron remained silent.
References for Leviticus 10:3
Moses summoned Mishael and Elzaphan, sons of Aaron's uncle Uzziel, and said to them, "Come here and carry your relatives away from the front of the sanctuary to [a place] outside the camp."
References for Leviticus 10:4
So they came forward and carried them in their tunics outside the camp, as Moses had said.
Then Moses said to Aaron and his sons Eleazar and Ithamar, "Do not let your hair hang loose and do not tear your garments, or else you will die, and the Lord will become angry with the whole community. However, your brothers, the whole house of Israel, may mourn over that tragedy when the Lord sent the fire.
References for Leviticus 10:6
You must not go outside the entrance to the tent of meeting or you will die, for the Lord's anointing oil is on you." So they did as Moses said.