וַיֵּט מֹשֶׁה אֶת יָדוֹ עַל הַשָּׁמַיִם וַיְהִי חֹשֶׁךְ אֲפֵלָה בְּכָל אֶרֶץ מִצְרַיִם שְׁלֹשֶׁת יָמִים. אָמְרוּ רַבּוֹתֵינוּ זִכְרוֹנָם לִבְרָכָה: שִׁבְעָה יָמִים שֶׁל חֹשֶׁךְ הָיוּ. כֵּיצַד? שְׁלֹשָׁה יָמִים הָרִאשׁוֹנִים מִי שֶׁהָיָה יוֹשֵׁב וּבִקֵּשׁ לַעֲמֹד, עוֹמֵד. וְהָעוֹמֵד שֶׁבִּקֵּשׁ לֵישֵׁב, יוֹשֵׁב. שְׁלֹשָׁה יָמִים הָאַחֲרוֹנִים, כָּל מִי שֶׁהָיָה יוֹשֵׁב, לֹא הָיָה יָכוֹל לַעֲמֹד. וְהָעוֹמֵד אֵינוֹ יָכוֹל לֵישֵׁב. וּמִי שֶׁהוּא רָבוּץ, לֹא הָיָה יָכוֹל לִזְקֹף. מִנַּיִן? שֶׁכֵּן כְּתִיב: לֹא רָאוּ אִישׁ אֶת אָחִיו, הֲרֵי שְׁלֹשָׁה. וְלֹא קָמוּ אִישׁ מִתַּחְתָּיו שְׁלֹשֶׁת יָמִים, הֲרֵי שִׁשָּׁה. And Moses stretched forth his hand toward heaven; and there was a thick darkness in all the land of Egypt three days (Exod. 10:22). Our sages maintained: There were seven days of darkness. During the first three days, a person who was sitting could stand if he wished to do so, and so too one who was standing could sit down. During the final three days, those who were sitting were unable to stand, those who were standing were unable to sit, and those who were reclining were unable to arise. Whence do we know this? From the fact that it is said; And they saw not one another for three days (ibid., v. 23). Hence for three days they could not change their positions, and for three days they could not arise from their places.
וְאֵי זֶה הוּא יוֹם הַשְּׁבִיעִי? וַיְהִי הֶעָנָן וְהַחֹשֶׁךְ וְגוֹ' וַיָּאֶר (שמות יד, כ). זֶה יוֹם שֶׁל יָם. וְכֵן בְּמִצְרַיִם, הֶעָנָן מֵאִיר לְיִשְׂרָאֵל וּמַחְשִׁיךְ לַמִּצְרִים, שֶׁנֶּאֱמַר: לֹא רָאוּ וְגוֹ' (שמות י, כב). What was the seventh day like? And there was the cloud and the darkness here, yet gave it light (Exod. 14:20). This light resembled the light experienced at the sea. Similarly in Egypt the cloud gave light to the Israelites but darkness to the Egyptians, as it is said: They saw not.
וּלְכָל בְּנֵי יִשְׂרָאֵל הָיָה אוֹר, וְהָיָה מֵאִיר לְיִשְׂרָאֵל וּמַרְאֶה לָהֶן כָּל כְּלֵי כֶּסֶף וְזָהָב וּשְׂמָלוֹת וְכָל טוּב מִצְרַיִם, וּמַה שֶּׁבַּתֵּבוֹת וּבֶחָבִיּוֹת וּבַמַּטְמוֹנִיּוֹת הָיָה מַרְאֶה לָהֶן. וְהָיוּ שׁוֹאֲלִין וְנוֹתְנִין לָהֶן בְּעַל כָּרְחָן, שֶׁהָיוּ אוֹמְרִים לָהֶם יִשְׂרָאֵל, הֲרֵי לְךָ בְּמָקוֹם פְּלוֹנִי כְּלִי כָּךְ וְכָךְ. הֱוֵי, וַיְהִי חֹשֶׁךְ אֲפֵלָה. All the children of Israel had light (ibid. 10:23). This implies that everything was illumined and disclosed to the Israelites—all the silver and gold utensils, the garments and the valuables of Egypt. Even the things that were in their boxes, barrels, and treasure chests were visible to them. And whatever the Israelites requested of them, they surrendered voluntarily, for the Israelites would say to them: “Behold, in that certain place you have such a utensil.” Hence, And there was a thick darkness.