וַיַּ֤עַל דָּוִד֙ וַֽאֲנָשָׁ֔יו וַֽיִּפְשְׁט֛וּ אֶל־הַגְּשׁוּרִ֥י והגרזי [וְהַגִּזְרִ֖י] וְהָעֲמָלֵקִ֑י כִּ֣י הֵ֜נָּה יֹשְׁב֤וֹת הָאָ֙רֶץ֙ אֲשֶׁ֣ר מֵֽעוֹלָ֔ם בּוֹאֲךָ֥ שׁ֖וּרָה וְעַד־אֶ֥רֶץ מִצְרָֽיִם׃
And David and his men went up, and made a raid upon the Geshurites, and the Gizrites, and the Amalekites; for those were the inhabitants of the land, who were of old, as thou goest to Shur, even unto the land of Egypt.
Read halakhic rulings (Jewish law) on I Samuel 27:8: and classical halakhic sources.