Rosh Hashanah 28A

שמע מקצת תקיעה בבור ומקצת תקיעה על שפת הבור ⁠— יצא. מקצת תקיעה קודם שיעלה עמוד השחר ומקצת תקיעה לאחר שיעלה עמוד השחר ⁠— לא יצא.

If one heard part of the blast in the pit and part of the blast at the edge of the pit, he has fulfilled his obligation. But if he heard part of the blast before dawn, when it is not yet time to sound the shofar, and part of the blast after dawn, he has not fulfilled his obligation.

אמר ליה אביי: מאי שנא התם ⁠— דבעינא כולה תקיעה בחיובא, וליכא. הכא נמי ⁠— בעינא כולה תקיעה בחיובא, וליכא!

Abaye said to him: What is different there, in the case of one who heard part of the blast before dawn and part of it after dawn? If you say that there the entire blast needs to be heard in a time of obligation, and when he hears part of the blast before dawn and part after dawn it is not all within the same time of obligation, here too, in the case of the pit, the entire blast needs to be in a place where one can fulfill his obligation, and when he hears part of the blast in a pit and part at the edge, it is not all within a place where he can fulfill his obligation.

הכי השתא?! התם ⁠— לילה לאו זמן חיובא הוא כלל, הכא ⁠— בור מקום חיובא הוא לאותן העומדין בבור.

The Talmud rejects this argument: How can these cases be compared? There, night is not a time of obligation at all, and sounding the shofar then has no meaning whatsoever, but here, a pit is a place of obligation for those standing in the pit. That is to say, the part of the blast that was heard in the pit is not inherently invalid, but merely disqualified due to an external factor, so that it is possible to connect it with the part of the blast that was heard at the edge of the pit.