Rif Brachot 13a

HIDE/SHOW IMAGE
13a

whether it is intended as obligatory or as voluntary it is forbidden.
For it is established for us that prayers {Shmoneh Esrei} were established corresponding to the temidim {daily 'olot - burnt offerings}, and just as the community may not bring freewill {nedava = voluntary} 'olot, so too the community may not pray freewill prayers. But the individual may pray a freewill prayer because an individual may bring a freewill 'olah.

Therefore, a person may not pray a musaf prayer as a freewill prayer, for one could not volunteer a musaf offering. And this that Rav Yehuda cited Shmuel:

If he was standing in prayer and he recalled that he had already prayed, he interrupts, even in the middle of a blessing,

the Sages explained it as, for example, he was praying with the intent that it be an obligatory prayer, and then forgot that he had prayed and stood to pray {again} with the intent of an obligatory prayer, and then recalled that he had already prayed, he interrupts, even in the middle of a blessing, for if he came to finish it, it would be as if he sacrificed two temidim in the morning, for which he would violate bal tosif {not to add to the commandments}, and therefore he interrupts, even in the middle of a blessing. And in this, even Rabbi Yochanan would admit, for Rabbi Yochanan only said "If only one could pray all day" with a voluntary prayer, such as tachanunim {entreaties} and the like, but an obligatory prayer he did not say.

Rav Yehuda cited Shmuel: One who prays and then enters shul and finds them praying, if he is able to come up with something new for his prayer such that his prayer will be entreaties {tachanunim} {the text marked in green seems an explanatory insertion into the text of the gemara by the Rif} he should pray, and if not, he should not pray.

Rav Nachman said: When we were in the house of Rabba bar Avuha, we had a question regarding these students who make a mistake and begin the weekday prayer on Shabbat whether they should finish {the prayer they started}. He said to us: they finish that blessing {that they are in the middle of}, for in reality, they need to pray 18, and because of the honor of Shabbat the Sages did not trouble him.

{Brachot 21b}
Rav Huna said: one who enters a shul and finds the congregation praying, if he is able to begin and finish before the shliach tzibur {agent of the congregation} reaches Modim, he should pray, and if not, he should not pray.

Rabbi Yehoshua ben Levi said: if he is able to begin and finish before the shliach tzibur {agent of the congregation} reaches Kedusha he should pray, and if not, he should not pray.

In what are they arguing? Rav Huna holds that an individual may say kiddush {=Kedusha}. And Rabbi Yehoshua ben Levi holds that an individual may not say kiddush.

And so did Rav Yitzchak say: an individual may not say kiddush {=kedusha}.

---

Rav Ada bar Ahava said: how do we know that an individual may not say kiddush {=kedusha}? For it states in Vayikra 22:32:

לב וְלֹא תְחַלְּלוּ, אֶת-שֵׁם קָדְשִׁי, וְנִקְדַּשְׁתִּי, בְּתוֹךְ בְּנֵי יִשְׂרָאֵל: אֲנִי ה, מְקַדִּשְׁכֶם.

32 And ye shall not profane My holy name; but I will be hallowed among the children of Israel: I am the LORD who hallow you,

any matter of sanctification should have no less then ten. The whole world {both opinions hold} that he does not interrupt {to answer kedusha}.

It was asked: may one interrupt for Amen Yehei Shemo HaGadol Mevorach?