כִּי֩ הָעֲמָלֵקִ֨י וְהַכְּנַעֲנִ֥י שָׁם֙ לִפְנֵיכֶ֔ם וּנְפַלְתֶּ֖ם בֶּחָ֑רֶב כִּֽי־עַל־כֵּ֤ן שַׁבְתֶּם֙ מֵאַחֲרֵ֣י יְהוָ֔ה וְלֹא־יִהְיֶ֥ה יְהוָ֖ה עִמָּכֶֽם׃
For there the Amalekite and the Canaanite are before you, and ye shall fall by the sword; forasmuch as ye are turned back from following the LORD, and the LORD will not be with you.’
Read halakhic rulings (Jewish law) on Numbers 14:43: and classical halakhic sources.