Parashas Shemos
וַתִּפְתַּח֙ וַתִּרְאֵ֣הוּ אֶת־הַיֶּ֔לֶד וְהִנֵּה־נַ֖עַר בֹּכֶ֑ה וַתַּחְמֹ֣ל עָלָ֔יו וַתֹּ֕אמֶר מִיַּלְדֵ֥י הָֽעִבְרִ֖ים זֶֽה׃
When she opened it, she saw that it was a child, a boy crying. She took pity on it and said, “This must be a Hebrew child.”
Torah Temimah points to R’ Yosei bar Chanina / R’ Yochanan — Sotah 12b (verified).
מילדי העברים זה — מנא ידעה? א״ר יוסי ב״ר חנינא: שראתה אותו מהול. \ldots א״ר יוחנן: מלמד שנתנבאה שלא מדעתה.
English: “Of the children of the Hebrews is this” — how did she know? R’ Yosei bar Chanina said: She saw that he was circumcised. R’ Yochanan said: This teaches that she prophesied without realizing it.
Custom
Bas Pharaoh recognized Moshe both by the sign of circumcision and by an unintended prophetic word.