וְאַ֤ף אֱלֹהִ֨ים ׀ עָ֘לָ֤ה בָהֶ֗ם וַֽ֭יַּהֲרֹג בְּמִשְׁמַנֵּיהֶ֑ם וּבַחוּרֵ֖י יִשְׂרָאֵ֣ל הִכְרִֽיעַ׃
When the anger of God went up against them, And slew of the lustieth among them, And smote down the young men of Israel.
Read halakhic rulings (Jewish law) on Psalms 78:31: and classical halakhic sources.