"And there was evening and there was morning, a third day" (Genesis 1:13) - on which mighty ones were created, as you say "captains and called men, all of them riding horses" (Ezekiel 23:23). When iron was created, the trees began to tremble. The Holy One, blessed be He, said to them: Let no tree of yours enter into it, and not one of you will be harmed.
The Trees That Trembled When Iron Was Made
Yalkut Shimoni on Torah 8:7
(בראשית א יג) וַיְהִי עֶרֶב וַיְהִי בֹקֶר יוֹם שְׁלִישִׁי, שְׁנִּבְרְאוּ בּוֹ גִּבּוֹרִים כְּהָאֵיךְ דְּאַתְּ אָמַר "שָׁלִשִׁים וּקְרוּאִים רֹכְבֵי סוּסִים כֻּלָם" כֵּיוָן שְׁנִּבְרָא בַּרְזֶל הִתְחִילוּ אִילָנוֹת מְרַתְּתִין. אָמַר לָהֶן הַקָּדוֹשׁ בָּרוּךְ הוּא, עֵץ מִכֶּם אַל יִכָּנֵס בּוֹ וְאֵין אֶחָד מִכֶּם נִזּוֹק.