Parashas Shemos
וַיִּ֖רֶף מִמֶּ֑נּוּ אָ֚ז אָֽמְרָ֔ה חֲתַ֥ן דָּמִ֖ים לַמּוּלֹֽת׃ {פ}
And when [God] let him alone, she added, “A bridegroom of blood because of the circumcision.”
Torah Temimah points to TT / Nedarim (verified).
למולות — מכאן לשתי מילות, אחת למילה ואחת לפריעה.
English: “For the circumcisions (lamulot)” — from here [we learn] of two acts of circumcision: one the milah itself and one the peri’ah.
Custom
Chazal derive the two stages of circumcision from the plural “mulot.”