I am seeking information on the origins of a key phrase in an East European Jewish incantation against the evil eye that circulated in both Hebrew and Yiddish versions. The phrase is "Three women stand on the crag of a rock" (Shalosh nashim omdot al shen ha-sela / Dray vayber zitsen oyf a shteyn).
The trope of "three women" was likely borrowed from medieval German and Polish Christian cults of three holy maidens or sisters, but I wonder if there is also a Jewish antecedent. The earliest versions of the spell that I have found date to the mid- or late 18th century. I am aware of the excellent work of Marek Tuszewicki on this incantation, but wonder if scholars of medieval and early modern Judaism are familiar with texts that mention three women or three sisters in a religious/magical context. (I'm aware of BT Niddah 59b but doubt there is a link.)