Rabbi Yochanan said: When Moses, Aaron, and the elders of Israel came and wished to enter, they saw around Pharaoh's palace such great multitudes that they trembled. Rabbi Meir said: The palace had four hundred gates, one hundred to each side, and at each one sat sixty thousand mighty men. Therefore the angel Gabriel came and brought them in. When Pharaoh saw them, he said, "What is the nature of these?" At once he summoned the gatekeepers: some he killed, some he flogged, some he removed and set others in their place. The next day they entered again before Pharaoh. He called the guards and said to them, "How do these men get in?" They said to him, "We do not know. They are sorcerers, for they do not enter by way of the gates." Immediately he told Aaron to cast down his staff, and it became a serpent. "Who is the LORD that I should heed His voice?" (Exodus 5:2). The Holy One, blessed be He, said to him: You said "Who [mi]"? By your life, by the sea [mi spelled backward is yam, sea] you will be struck; at the sea you will know who I am. You said, "I do not know the LORD." By your life, tomorrow you will say, "The LORD is the righteous one" (Exodus 9:27). You said, "I will also not let Israel go." By your life, tomorrow you will take each one by the hand to send him out, as it is said, "And it came to pass when Pharaoh let the people go" (Exodus 13:17).
Gabriel Opens the Guarded Gates of Pharaoh's Palace
Yalkut Shimoni on Torah 175:2
אָמַר רַבִּי יוֹחָנָן, לְפִי שֶׁבָּאוּ מֹשֶׁה וְאַהֲרֹן וְזִקְנֵי יִשְׂרָאֵל וְרָצוּ לִכָּנֵס, רָאוּ סְבִיב פְּלָטִין שֶׁלּוֹ כַּמָּה אוּכְלוּסִים, וְנִזְדַּעְזְעוּ. אָמַר רַבִּי מֵאִיר, אַרְבַּע מֵאוֹת פְּתָחִים הָיוּ לַפְּלָטִין, מֵאָה לְכָל רוּחַ, וְעַל כָּל אֶחָד יָשְׁבוּ שִׁישִׁים אֶלֶף גִּבּוֹרִים, לְפִיכָךְ בָּא גַּבְרִיאֵל וְהִכְנִיסָן. כֵּיוָן שֶׁרָאָה פַּרְעֹה אוֹתָן, אָמַר מַה טִיבָן שֶׁל אֵלּוּ, מִיָּד הֵבִיא שׁוֹמְרֵי הַפְּתָחִים, מֵהֶן הָרַג, מֵהֶן הִלְקָה, מֵהֶן הֶעֱבִיר וְהֶעֱמִיד אֲחֵרִים תַּחְתֵּיהֶן. שׁוּב לְמָחָר נִכְנְסוּ לִפְנֵי פַּרְעֹה, קָרָא לַשּׁוֹמְרִים אָמַר לָהֶם הֵיאַךְ אֵלּוּ נִכְנָסִין, אָמְרוּ לֵיהּ אֵין אָנוּ יוֹדְעִין, כַּשְׁפָנִים הֵם, שֶׁדֶּרֶךְ פְּתָחִים אֵינָן נִכְנָסִין. מִיָּד אָמַר לְאַהֲרֹן שֶׁיַּשְׁלִיךְ מַטֵּהוּ, וְנַעֲשָׂה נָחָשׁ. מִי ה' אֲשֶׁר אֶשְׁמַע בְּקֹלוֹ, אָמַר לֵיהּ הַקָּדוֹשׁ בָּרוּךְ הוּא, אַתָּה אָמַרְתָּ מִי, חַיֶּיךָ בְּמִי אַתָּה לוֹקֶה, מֵי, יָם לְמַפְרֵעַ, בַּיָּם אַתָּה יוֹדֵעַ מִי אֲנִי. אַתָּה אָמַרְתָּ לֹא יָדַעְתִּי אֶת ה', חַיֶּיךָ לְמָחָר אַתָּה אוֹמֵר "ה' הַצַּדִּיק", אַתָּה אָמַרְתָּ וְגַם אֶת בְּנֵי יִשְׂרָאֵל לֹא אֲשַׁלֵּחַ, חַיֶּיךָ לְמָחָר אַתָּה אוֹחֵז בְּיַד כָּל אֶחָד לְשַׁלְּחוֹ, שֶׁנֶּאֱמַר (שמות יג, יז) "וַיְהִי בְּשַׁלַּח פַּרְעֹה".