וְעַתָּ֗ה שְׁלַ֤ח הָעֵז֙ אֶֽת־מִקְנְךָ֔ וְאֵ֛ת כָּל־אֲשֶׁ֥ר לְךָ֖ בַּשָּׂדֶ֑ה כָּל־הָאָדָ֨ם וְהַבְּהֵמָ֜ה אֲשֶֽׁר־יִמָּצֵ֣א בַשָּׂדֶ֗ה וְלֹ֤א יֵֽאָסֵף֙ הַבַּ֔יְתָה וְיָרַ֧ד עֲלֵהֶ֛ם הַבָּרָ֖ד וָמֵֽתוּ׃
Donc, fais rassembler ton bétail et tout ce que tu as dans les champs. Tout homme ou animal qui se trouvera dans les champs et ne sera pas rentré dans les maisons, sera atteint de la grêle et périra.’ "
Or HaChaim
וישם ה׳ מועד לאמור, G'd appointed a set time, etc. He informed the Egyptians of when the plague would strike to enable them to bring their livestock indoors as we also find when the plague of hail struck (9,19). In that instance G'd told the Egyptians outright to bring their animals indoors to protect them, whereas here He only hinted at this. The hint is expressed in the Torah by the word לאמור. This meant that Moses and Aaron were to inform both Pharaoh and the Egyptians of the timing of that plague.
Rashi
assemble Heb. העיזו. Comp. “Send, gather (העז)” (Exodus 9:19).
Siftei Chakhamim
טבוח is not an imperative for then it should have said וטבח. And then it would be like (Shemos 4:4): שלח ידך (Stretch out your hand), and (Shemos 9:19): שלח העז (Now send word and gather), which are imperatives.
Rashi
אסף [GOD] HATH TAKEN AWAY [MY DISGRACE] — He has laid it up somewhere where it cannot be seen. Similar examples are (Isaiah 4:1) “Take thou away (אסוף) our reproach”; (Exodus 9:19) “and shall not have been taken away (יאסף) into the house “; (Joel 4:13) “withdraw (אספו) their shining”; (Isaiah 60:20) “neither shall thy moon withdraw itself (יאסף) — meaning shall not hide itself.