וַיֹּ֨אמֶר יְהוָ֜ה אֶל־מֹשֶׁ֗ה נְטֵ֨ה יָדְךָ֜ עַל־אֶ֤רֶץ מִצְרַ֙יִם֙ בָּֽאַרְבֶּ֔ה וְיַ֖עַל עַל־אֶ֣רֶץ מִצְרָ֑יִם וְיֹאכַל֙ אֶת־כָּל־עֵ֣שֶׂב הָאָ֔רֶץ אֵ֛ת כָּל־אֲשֶׁ֥ר הִשְׁאִ֖יר הַבָּרָֽד׃
L’Éternel dit à Moïse." Étends ta main sur le pays d’Égypte pour les sauterelles, afin qu’elles envahissent le pays d’Égypte et qu’elles dévorent tout l’herbage de la terre, tout ce qu’a épargné la grêle."
Makkot
And they both derive their views from [the same statement] of Rebbi Yehudah. For It was taught in a barasia, (Exodus 12, 10) "And do not leave anything over until morning. And anything leftover until morning [must be burned in fire] etc." the Torah comes to give a positive commandment following a negative commandment to teach that he is not liable to malkus. These are the words of Rebbi Yehudah. Rebbi Yochanon expounds thus, the reason [Rebbi Yehudah says that he isn't flogged] is because the Torah comes [with a remedial positive commandment], but if the Torah would not have came then he would be flogged. We therefore see that a questionable warning constitutes as a valid warning.