Parashas Vaeira
וַיַּשְׁלִ֙יכוּ֙ אִ֣ישׁ מַטֵּ֔הוּ וַיִּהְי֖וּ לְתַנִּינִ֑ם וַיִּבְלַ֥ע מַטֵּֽה־אַהֲרֹ֖ן אֶת־מַטֹּתָֽם׃
each cast down his rod, and they turned into serpents. But Aaron’s rod swallowed their rods.
Torah Temimah points to R’ Elazar — Shabbos 97a (verified).
ויבלע מטה אהרן — א״ר אלעזר: נס בתוך נס.
English: “And the staff of Aharon swallowed” — R’ Elazar said: A miracle within a miracle.
Custom
Chazal teach that the swallowing was a miracle within a miracle: a staff, not a serpent, consumed the other staffs.