Mishnayos Tamid Perek 7 Mishnah 1

After the priests concluded sacrificing the daily morning offering, they would enter the Sanctuary to prostrate themselves. On occasions when the High Priest would enter the Sanctuary to prostrate himself, he would enter before the other priests. When the High Priest enters the Sanctuary, three priests hold him to assist him and support him, in order to distinguish the service of the High Priest from that of the other priests entering the Sanctuary. One priest held his right hand and one priest held his left hand, and one priest stood behind the High Priest, holding onto the two precious onyx stones located on the shoulders of the High Priest, on the ephod. And once the appointed priest heard the sound from the feet of the High Priest, produced by the bells attached to the bottom of his robe, he knew that the High Priest was emerging from the Sanctuary, and he lifted the curtain suspended at the opening of the Entrance Hall for him, to facilitate his exit. After the High Priest entered and prostrated himself and emerged from the Sanctuary, his brethren the priests entered, prostrated themselves, and emerged from the Sanctuary.

בִּזְמַן שֶׁכֹּהֵן גָּדוֹל נִכְנָס לְהִשְׁתַּחֲווֹת, שְׁלשָׁה אוֹחֲזִין בּוֹ, אֶחָד בִּימִינוֹ, וְאֶחָד בִּשְׂמֹאלוֹ, וְאֶחָד בַּאֲבָנִים טוֹבוֹת. וְכֵיוָן שֶׁשָּׁמַע הַמְמֻנֶּה קוֹל רַגְלָיו שֶׁל כֹּהֵן גָּדוֹל שֶׁהוּא יוֹצֵא, הִגְבִּיהַּ לוֹ אֶת הַפָּרֹכֶת, נִכְנַס וְהִשְׁתַּחֲוָה וְיָצָא, וְנִכְנְסוּ אֶחָיו הַכֹּהֲנִים וְהִשְׁתַּחֲווּ וְיָצָאוּ: