The Genizah of the Ben Ezra synagogue in Fustat preserved dozens of petitions addressed to the Fatimid and Ayyubid chanceries in Cairo and decrees that they issued in response. This article provides an edition, translation, and discussion of a petition housed among the Genizah documents of the Bodleian Library directed to Sitt al-Mulk, half-sister of the caliph al-Ḥākim (386–411/996–1021) and head of the Fatimid state between his death and her own in 414/1023. Geoffrey Khan had previously identified two petitions to a Fatimid princess housed in Cambridge and New York; it is likely that they, too, were addressed to Sitt al-Mulk. Such documents elucidate Sitt al-Mulk's role in government after her brother's death and provide evidence for the chronicler al-Musabbiḥī's claim that she received and responded to petitions from subjects. The article offers possible explanations as to why petitions such as this one, which concerns an Ismaili mosque, should have found their way to the Jewish community of Fustat whose members reused and preserved them. It also suggests some broader conclusions about the dispersal, survival, or disappearance of pre-Ottoman Middle Eastern archives and documents.