וְהִפְלֵיתִי֩ בַיּ֨וֹם הַה֜וּא אֶת־אֶ֣רֶץ גֹּ֗שֶׁן אֲשֶׁ֤ר עַמִּי֙ עֹמֵ֣ד עָלֶ֔יהָ לְבִלְתִּ֥י הֱיֽוֹת־שָׁ֖ם עָרֹ֑ב לְמַ֣עַן תֵּדַ֔ע כִּ֛י אֲנִ֥י יְהוָ֖ה בְּקֶ֥רֶב הָאָֽרֶץ׃
And I will set apart in that day the land of Goshen, in which My people dwell, that no swarms of flies shall be there; to the end that thou mayest know that I am the LORD in the midst of the earth.
Read halakhic rulings (Jewish law) on Exodus 8:18: and classical halakhic sources.