וַיֹּ֤אמֶר יְהוָה֙ אֶל־מֹשֶׁ֔ה רֵ֖ד הָעֵ֣ד בָּעָ֑ם פֶּן־יֶהֶרְס֤וּ אֶל־יְהוָה֙ לִרְא֔וֹת וְנָפַ֥ל מִמֶּ֖נּוּ רָֽב׃
And the LORD said unto Moses: ‘Go down, charge the people, lest they break through unto the LORD to gaze, and many of them perish.
Read halakhic rulings (Jewish law) on Exodus 19:21: and classical halakhic sources.