יומא ז׳Yoma 7

Mishnah 1א׳

בָּא לוֹ כֹהֵן גָּדוֹל לִקְרוֹת. אִם רָצָה לִקְרוֹת בְּבִגְדֵי בוּץ, קוֹרֵא. וְאִם לֹא, קוֹרֵא בְאִצְטְלִית לָבָן מִשֶּׁלּוֹ. חַזַּן הַכְּנֶסֶת נוֹטֵל סֵפֶר תּוֹרָה וְנוֹתְנוֹ לְרֹאשׁ הַכְּנֶסֶת, וְרֹאשׁ הַכְּנֶסֶת נוֹתְנוֹ לַסְּגָן, וְהַסְּגָן נוֹתְנוֹ לְכֹהֵן גָּדוֹל, וְכֹהֵן גָּדוֹל עוֹמֵד וּמְקַבֵּל וְקוֹרֵא עוֹמֵד, וְקוֹרֵא אַחֲרֵי מוֹת וְאַךְ בֶּעָשׂוֹר. וְגוֹלֵל סֵפֶר תּוֹרָה וּמַנִּיחוֹ בְחֵיקוֹ, וְאוֹמֵר, יוֹתֵר מִמַּה שֶּׁקָּרָאתִי לִפְנֵיכֶם כָּתוּב כָּאן, וּבֶעָשׂוֹר שֶׁבְּחֻמַּשׁ הַפְּקוּדִים קוֹרֵא עַל פֶּה, וּמְבָרֵךְ עָלֶיהָ שְׁמֹנֶה בְרָכוֹת, עַל הַתּוֹרָה, וְעַל הָעֲבוֹדָה, וְעַל הַהוֹדָאָה, וְעַל מְחִילַת הֶעָוֹן, וְעַל הַמִּקְדָּשׁ בִּפְנֵי עַצְמוֹ, וְעַל יִשְׂרָאֵל בִּפְנֵי עַצְמָן וְעַל יְרוּשָׁלַיִם בִּפְנֵי עַצְמָהּ וְעַל הַכֹּהֲנִים בִּפְנֵי עַצְמָן וְעַל שְׁאָר הַתְּפִלָּה:

The High Priest then came to read [the Torah portion for the day]. He could read either wearing linen garments, or his own white robe. The synagogue attendant would take the Torah scroll, and hand it to the head of the synagogue, and the head of the synagogue would hand it to the assistant [High Priest] and the assistant would hand it over to the High Priest. The High Priest would stand, and receive it, and read "After the death" (Leviticus 16:1-34) and "On the tenth" (Leviticus 23:26-36). Then he would roll up the scroll, hold it close to his bosom, and say, "More than that which I have read before you, is written here." He would then recite by heart “On the tenth day" (Numbers 29:7-11). He recites over it eight blessings: for the Torah, for the Temple Service, for thanksgiving, for the forgiveness of sins, and for the Temple separately, and for Israel separately, and for Jerusalem separately, for the priests separately, and for the rest of the prayer.

Mishnah 2ב׳

הָרוֹאֶה כֹהֵן גָּדוֹל כְּשֶׁהוּא קוֹרֵא, אֵינוֹ רוֹאֶה פַר וְשָׂעִיר הַנִּשְׂרָפִים. וְהָרוֹאֶה פַר וְשָׂעִיר הַנִּשְׂרָפִים, אֵינוֹ רוֹאֶה כֹהֵן גָּדוֹל כְּשֶׁהוּא קוֹרֵא. וְלֹא מִפְּנֵי שֶׁאֵינוֹ רַשַּׁאי, אֶלָּא שֶׁהָיְתָה דֶרֶךְ רְחוֹקָה, וּמְלֶאכֶת שְׁנֵיהֶן שָׁוָה כְאֶחָת:

The one who sees the High Priest while he is reading does not see the bull and he-goat that are burned, and the one seeing the bull and the he-goat being burned does not see the High Priest while he is reading. Not because it is prohibited to do so, but because the distance between the two areas was great, and both rituals were performed simultaneously.