Numbers 26:61 Kabbalah

וַיָּ֥מָת נָדָ֖ב וַאֲבִיה֑וּא בְּהַקְרִיבָ֥ם אֵשׁ־זָרָ֖ה לִפְנֵ֥י יְהוָֽה׃

And Nadab and Abihu died, when they offered strange fire before the LORD.

Read kabbalistic (mystical) interpretation of Numbers 26:61: and classical mystical sources.