The King James Version of Asa-Ra

Two sons of Aaron take the censor and put fire in it, a term that just means coals of fire and lay incense on it. They offer unauthorized fire before the Lord, which is a good translation because he had not commanded them. So they do something that they were not commanded to do. The text doesn't really specify the offense committed by the two priests but it just says that they did something that had not been specifically ordained. In other words, it wasn't part of the procedure.