"And it shall be for you to keep" (Exodus 12:6): Scripture tells that they would inspect it four days before its slaughter. From here you may reason about the daily offering: "keeping" is stated regarding the Passover, and "keeping" is stated regarding the daily offering. Just as the keeping stated regarding the Passover means they inspect it four days before its slaughter, so too the keeping stated regarding the daily offering means they inspect it four days before its slaughter. From here they said: they keep no fewer than six inspected lambs in the Chamber of Lambs, enough for a Sabbath and the two festival days of the New Year, and one always adds to them. If on the eve of festivals the daily and additional offerings are many -- but this teacher is speaking generally, only of the daily offerings, and what does "enough for a Sabbath" mean? It is merely a sign, and this is what he says: they keep no fewer than six inspected lambs in the Chamber of Lambs four days before slaughter. And who is this teacher? It is Ben Bag Bag, for it is taught: from where do we learn that the daily offering requires inspection, and so on. It is also precise, for it teaches "enough for a Sabbath" and does not teach "for a Sabbath" -- learn from this. "And it shall be for you to keep" excludes the Passover of the generations, for the Passover of Egypt was taken from the tenth, while the Passover of the generations is taken at any time. "On the tenth of this month" -- this one is taken from the tenth, but the Passover of the generations is not taken from the tenth. "And it shall be for you to keep until the fourteenth day of this month." Why do I need "this"? To exclude the second Passover, of which a similar wording is written in the portion of Beha'alotekha.
Inspecting the Lamb Four Days and the Lambs of the Daily Offering
Yalkut Shimoni on Torah 195:2
וְהָיָה לָכֶם לְמִשְׁמֶרֶת, מַגִּיד הַכָּתוּב שֶׁהָיוּ מְבַקְּרִין אוֹתוֹ אַרְבָּעָה יָמִים קֹדֶם לִשְׁחִיטָתוֹ, מִכָּאן אַתָּה דָּן עַל הַתָּמִיד, נֶאֱמַר שְׁמִירָה בְּפֶסַח וְנֶאֱמַר שְׁמִירָה בְּתָמִיד, מַה שְׁמִירָה הָאֲמוּרָה בְּפֶסַח מְבַקְּרִין אוֹתוֹ אַרְבָּעָה יָמִים קֹדֶם לִשְׁחִיטָתוֹ, אַף שְׁמִירָה הָאֲמוּרָה בְּתָמִיד מְבַקְּרִין אוֹתוֹ אַרְבָּעָה יָמִים קֹדֶם לִשְׁחִיטָתוֹ. מִכָּאן אָמְרוּ, אֵין פּוֹחֲתִין מִשִּׁשָׁה טְלָאִים הַמְּבֻקָּרִים בְּלִשְׁכַּת הַטְּלָאִים, כְּדֵי לְשַׁבָּת וּשְׁנֵי יָמִים טוֹבִים שֶׁל רֹאשׁ הַשָּׁנָה וּמוֹסִיפִין לְעוֹלָם. (אִי בְּעַרְבֵי) תְּמִידִין וּמוּסָפִין טוּבָא הַוֵי. וְהַאי תָּנָא בְּעָלְמָא קָאי, אַתְּמִידִין לְחוּדַיְיהוּ קָאי וּמַאי כְּדֵי לְשַׁבָּת, סִימָנָא בְּעָלְמָא וְהֲכִי קָאָמַר, אֵין פּוֹחֲתִין מִשִּׁשָׁה טְלָאִים הַמְּבֻקָּרִין בְּלִשְׁכַּת הַטְּלָאִים אַרְבָּעָה יָמִים קֹדֶם שְׁחִיטָה, וּמַנִי בֶּן בַּג בַּג הִיא, דְּתֲנְיָא, מִנַּיִן לְתָמִיד שֶׁטָּעוּן בִקּוּר וְכוּ'. דַּיְקָא נַמִי דְּקְתַּנִי כְּדֵי לְשַׁבָּת וְלֹא קְתַנִי לְשַׁבָּת, שְׁמַע מִינָּהּ. וְהָיָה לָכֶם לְמִשְׁמֶרֶת לְהוֹצִיא פֶּסַח דּוֹרוֹת, שֶׁפֶּסַח מִצְרַיִם מִקְּחוֹ מִבֶּעָשׂוֹר וּפֶסַח דּוֹרוֹת מִקְּחוֹ בְּכָל זְמַן. בֶּעָשׂוֹר לַחֹדֶשׁ הַזֶּה, זֶה מִקְּחוֹ מִבֶּעָשׂוֹר וּפֶסַח דּוֹרוֹת אֵין מִקְּחוֹ מִבֶּעָשׂוֹר. וְהָיָה לָכֶם לְמִשְׁמֶרֶת עַד אַרְבָּעָה עָשָׂר יוֹם לַחֹדֶשׁ הַזֶּה. הַזֶּה לָמָּה לִי, לִמְעוּטֵי פֶּסַח שֵׁנִי דִּכְוָותֵיהּ כְּתִיב בְּפָרָשַׁת בְּהַעֲלֹתְךָ.