אורח חיים קכ״דOrach Chayim 124

Se’if 1א׳

לְאַחַר שֶׁסִיְּמוּ הַצִּבּוּר תְּפִלָּתָן, יַחֲזֹר שְׁלִיחַ צִבּוּר הַתְּפִלָּה, שֶׁאִם יֵשׁ מִי שֶׁאֵינוֹ יוֹדֵעַ לְהִתְפַּלֵּל יְכַוֵּן לְמַה שֶּׁהוּא אוֹמֵר, וְיוֹצֵא בוֹ; וְצָרִיךְ אוֹתוֹ שֶׁיּוֹצֵא בִּתְפִלַּת שְׁלִיחַ צִבּוּר לְכַוֵּן לְכָל מַה שֶּׁאוֹמֵר שְׁלִיחַ צִבּוּר מֵרֹאשׁ וְעַד סוֹף; וְאֵינוֹ מַפְסִיק; וְאֵינוֹ מֵשִׂיחַ; וּפוֹסֵעַ ג' פְּסִיעוֹת לְאַחֲרָיו, כְּאָדָם שֶׁמִּתְפַּלֵּל לְעַצְמוֹ.

Laws of the Conduct of the Prayer Leader during the Eighteen Blessings [i.e. Amidah], and the Laws of Answering Amen. Containing 12 S'ifim: After the congregation finishes their prayer [i.e. Amidah], the prayer leader repeats the prayer, so that if there is anyone who does not know how to pray [the Amidah], [that person] will pay attention to what [the prayer leader] is saying and fulfill [that person's] obligation through that. And that one who is fulfilling an obligation through the prayer of the prayer leader must pay attention to everything that [the prayer leader] says, from beginning to end, and may not interrupt and may not converse, and [that person] steps three steps backwards just like one who prays by oneself.

Se’if 2ב׳

שְׁלִיחַ צִבּוּר שֶׁנִּכְנַס לְבֵית הַכְּנֶסֶת וּמָצָא צִבּוּר שֶׁהִתְפַּלְּלוּ בְּלַחַשׁ, וְהוּא צָרִיךְ לַעֲמֹד לִפְנֵי הַתֵּבָה לְאַלְתַּר, יוֹרֵד לִפְנֵי הַתֵּבָה וּמִתְפַּלֵּל בְּקוֹל רָם לַצִּבּוּר, וְאֵינוֹ צָרִיךְ לַחֲזֹר וּלְהִתְפַּלֵּל בְּלַחַשׁ. הַגָּה: וְכֵן אִם הוּא שְׁעַת הַדַּחַק, כְּגוֹן שֶׁיָּרֵא שֶׁיַּעֲבֹר זְמַן הַתְּפִלָּה, יוּכַל לְהִתְפַּלֵּל מִיָּד בְּקוֹל רָם, וְהַצִּבּוּר מִתְפַּלְּלִין עִמּוֹ מִלָּה בְּמִלָּה בְּלַחַשׁ עַד לְאַחַר הָאֵל הַקָּדוֹשׁ, וְטוֹב שֶׁיִּהְיֶה אֶחָד לְכָל הַפָּחוֹת שֶׁיַּעֲנֶה אָמֵן אַחַר הַשְּׁלִיחַ צִבּוּר (מַהֲרִי"ל).

A prayer leader who entered the synagogue and found the congregation praying the quiet [Amidah] prayer, and needs to "pass before the Ark" [i.e. needs to get in position to lead the repetition] immediately - [the prayer leader] goes down before Ark [i.e. takes the leader's position] and prays aloud for the congregation, and does not need to go back and pray quietly. Rema: And so too, if there's a pressing circumstance, for example, [the leader] is afraid that the time of prayer will pass, [the leader] may pray aloud immediately and the congregation prays with [the leader] word for word quietly until after [the blessing of] "Hakeil Hakadosh". And it would be good if there is at least one person [available to] answer Amen after the blessings of the prayer leader. [Mahari"l]

Se’if 3ג׳

קָהָל שֶׁהִתְפַּלְּלוּ וְכֻלָּם בְּקִיאִים בַּתְּפִלָּה, אַף עַל פִּי כֵן יֵרֵד שְׁלִיחַ צִבּוּר וְחוֹזֵר לְהִתְפַּלֵּל, כְּדֵי לְקַיֵּם תַּקָּנַת חֲכָמִים. הַגָּה: וְאִם יֵשׁ יְחִידִים בַּקָּהָל מַאֲרִיכִין בִּתְפִלָּתָן, אֵין לַשְּׁלִיחַ צִבּוּר לְהַמְתִּין עֲלֵיהֶם וַאֲפִלּוּ הָיוּ חֲשׁוּבֵי הָעִיר; וְכֵן אִם הָיָה מִנְיָן בְּבֵית הַכְּנֶסֶת, אֵין לְהַמְתִּין עַל אָדָם חָשׁוּב אוֹ גָּדוֹל שֶׁעֲדַיִן לֹא בָּא (בִּנְיָמִין זְאֵב סי' קס"ח).

A congregation which prayed [the Amidah] and all of them are experts in prayer [themselves] - nevertheless, the prayer leader should descend [to lead] and go back to pray in order to maintain the decree of our Sages. Gloss: And if there are individuals amongst the congregation who are prolonging their prayers, the prayer leader should not wait for them, even if they are the prominent people of the city. And so too, if there was a quorum in the synagogue, they should not wait for a prominent or great person who still has not yet arrived. [Binyamin Ze'ev Siman 168)