Berakhot 23A

מר סבר: אם שהה כדי לגמור את כולה ⁠— חוזר לראש. ומר סבר: למקום שפסק.

One Sage held that, as a rule, if one interrupted his prayer and delayed continuing his prayer for an interval sufficient to complete the entire prayer, he returns to the beginning of the prayer. And one Sage held: He returns to the place in the prayer where he stopped.

אמר רב אשי: האי ״אם שהה״, אם לא שהה מיבעי ליה! אלא, דכולי עלמא אם שהה כדי לגמור את כולה ⁠— חוזר לראש, והתם בדלא שהה קמיפלגי, דמר סבר גברא דחויא הוא, ואין ראוי, ואין תפלתו תפלה. ומר סבר גברא חזיא הוא, ותפלתו תפלה.

Rejecting this possibility, Rav Ashi said: If that was the crux of their dispute, they should have discussed the element of: If he delayed, and: If he did not delay. Nowhere in their dispute do they mention the matter of how long the delay was for. Rather, everyone, both Rav Ḥisda and Rav Hamnuna, agrees that if one delayed continuing his prayer for an interval sufficient to complete the entire prayer, he returns to the beginning of the prayer. And there, in the dispute under discussion, they disagree with regard to one who did not delay that long. The dispute centers on the status of the one praying in this particular case. As one Sage holds that since he evidently needed to urinate before starting his prayer, he is a man who was disqualified, and unfit for prayer, and his prayer is not a valid prayer; therefore he must repeat it in its entirety. And one Sage holds he is a man who was fit for prayer and his prayer is a valid prayer.

תנו רבנן: הנצרך לנקביו ⁠— אל יתפלל, ואם התפלל ⁠— תפלתו תועבה. אמר רב זביד ואיתימא רב יהודה: לא שנו אלא שאינו יכול לשהות בעצמו, אבל אם יכול לשהות בעצמו ⁠— תפלתו תפלה.

A baraita states: One who needs to relieve himself may not pray, and if he prayed, his prayer is an abomination. Rav Zevid and some say Rav Yehuda said in qualifying this statement: They only taught this halakha in a case where one cannot restrain himself. But, if he can restrain himself, his prayer is a valid prayer as he is not tarnished by his need to relieve himself.