א הַנִּכְנָס לְבֵית הַכְּנֶסֶת וּמָצָא צִבּוּר מִתְפַּלְּלִין, אִם יָכוֹל לְהַתְחִיל וְלִגְמֹר קֹדֶם שֶׁיַּגִּיעַ שְׁלִיחַ צִבּוּר לִקְדֻשָּׁה אוֹ לְקַדִּישׁ, יִתְפַּלֵּל. וְהוּא הַדִּין אָמֵן דְּהָאֵל הַקָּדוֹשׁ וְשׁוֹמֵעַ תְּפִלָּה, דִּינָן כְּקַדִּישׁ וּקְדֻשָּׁה (תוס' וְהָרֹא"שׁ וּמָרְדְּכַי פֶּרֶק מִי שֶׁמֵּתוֹ וּתְרוּמַת הַדֶּשֶׁן סי' י"א). וְאִם לָאו, אַל יִתְפַּלֵּל אִם אֵין הַשָּׁעָה עוֹבֶרֶת; וְאִם נִכְנַס אַחַר קְדֻשָּׁה, אִם יָכוֹל לְהַתְחִיל וְלִגְמֹר קֹדֶם שֶׁיַּגִּיעַ שְׁלִיחַ צִבּוּר לְמוֹדִים, יִתְפַּלֵּל, וְאִם לָאו אַל יִתְפַּלֵּל; וְהוּא הַדִּין אִם יָכוֹל לְהַגִּיעַ לְמוֹדִים, אוֹ לְאַחַת מֵהַבְּרָכוֹת שֶׁשּׁוֹחִים בָּהֶם, כְּשֶׁיַּגִּיעַ שְׁלִיחַ צִבּוּר לְמוֹדִים, יִתְפַּלֵּל; וְאִם צָרִיךְ לְהַתְחִיל כְּדֵי לִסְמֹךְ גְּאֻלָּה לִתְפִלָּה, וְנִזְדַּמֵּן לוֹ שֶׁמַּגִּיעַ שְׁלִיחַ צִבּוּר לְמוֹדִים כְּשֶׁהוּא בְּאַחַת הַבְּרָכוֹת (בְּאֶמְצָעָהּ), יִשְׁחֶה עִמּוֹ; אֲבָל אִם הוּא בִּתְחִלָּתָהּ אוֹ בְּסוֹפָהּ, לֹא יִשְׁחֶה, שֶׁאֵין שׁוֹחִין בִּתְחִלַּת בְּרָכָה אוֹ בְּסוֹפָהּ, אֶלָּא בְּאָבוֹת וּבְהוֹדָאָה.
1 The Law Regarding How An Individual Should Conduct Themselves In Order To Focus Their Prayer [Together] With The Congregation, Containing 3 Se'ifim: One who enters the synagogue and finds the congregation praying, if one is able to start and finish [one's Amidah] before the the prayer leader arrives at Kedushah [the third blessing of the Amidah] or Kaddish, one should pray. [And this is [also] the ruling for [answering] Amen to [the blessings of] "The Holy One" [at the end of the third Amidah blessing] and "Who Hears Prayer" [at the end of the third-to-last Amidah blessing]; their law is like Kaddish and Kedusha [Tosefot, the Ro"sh, and the Mordecai in the chapter "Mi Shemeito" [Tractate Berakhot, chp. 3], and Terumat Hadeshen siman 11] and if not, one should not pray if [i.e., as long as] the time [for praying the Amidah] has not [yet] passed. And if one entered after [the congregation recited] Kedushah, if one is able to start and finish [one's Amidah] before the prayer leader arrives at Modim [the second-to-last blessing of the Amidah], one should pray; and if not, one should not pray. And this is the ruling if [as long as] one is able to arrive at Modim or one of the other blessings in which one bows: when the prayer leader arrives at Modim, one should pray. And if one needs to begin [praying the Amidah] in order to juxtapose Geulah [the blessing of redemption that immediately precedes the Amidah] to the [Amidah] prayer, and it happens that the prayer leader reaches Modim when one is in the middle of one of the [Amidah] blessings, one should bow with [the prayer leader]. But if one is at the beginning or end [of one of the Amidah blessings], one should not bow, because we do not bow at the beginning or end of a blessing, except for Avot [the first blessing of the Amidah] and Hoda'ah [the second-to-last blessing of the Amidah].