TT #713 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:07
And if the man does not desire to take his yevamah, then his yevamah shall go up to the gate to the elders and say: “My husband’s brother refuses to establish a name for his brother in Israel; he will not perform the duty of a husband’s brother for me.”
Torah Temimah points to Sifrei / Yevamot 101b.
TT lemma: אֶל הַזְּקֵנִים.
אֶל הַזְּקֵנִים – זִקְנֵי שָׁנִים; וְאֵין בֵּית דִּין שָׁקוּל, מוֹסִיפִים עוֹד אֶחָד – הֲרֵי שְׁלֹשָׁה; מִכָּאן דְּמִצְוַת חֲלִיצָה בִּשְׁלֹשָׁה דַּיָּנִים. וּלְכַתְּחִלָּה מִצְוָה לְצָרֵף עוֹד שְׁנַיִם וְיִהְיוּ חֲמִשָּׁה.
English: “To the elders” — elders in years; a court may not be even, therefore they add one more — behold three; from here that the mitzvah of chalitzah requires three judges. And preferably they add two more so that there are five.
On the daf / in context: Three is the minimum competent court; five is preferred for greater publicity that she is a chalutzah.
Derash establishing the size of the chalitzah court.
Chalitzah requires a minimum of three judges; five are preferred for publicity.