In 1558, three Muslims left their homes in the Grand Duchy of Lithuania and set out on hajj. The journey of these “Lipka Tatars” south to Mecca and Medina, some four-thousand kilometers as the crow flies, took them first to the Ottoman capital in Istanbul where they were approached by Grand Vizier Rüstem Pasha, who asked them to create an account of the history and condition of the Muslim community in “Lehistan”, or Poland-Lithuania, for Sultan Süleymân I (r. 1520-1566). The resulting work, the Risâle-i Tatar-i Leh, was composed with the help of the Ottoman Ulema and is a rare and invaluable account of Christian Europe’s largest integrated Muslim population in a thoroughly Ottoman context. In it, we learn how members of Süleymân’s court envisioned Polish-Lithuanian Muslims as a branch of the Islamic ecumene, the local legal status Muslims in the dâr al-harb, their patrimony and social hierarchies, details regarding the religious practices of Muslims in the region, and the responsibilities of the Ottoman Sultan as the Khādim al-Haramayn al-Şarifayn (protector of the Mecca and Medina) vis-á-vis Muslims living permanently outside the lands of the dâr al-Islâm. Because the Risâle-i Tatar-i Leh was produced in the Ottoman court, it was also a tool for legitimizing the sultan’s claim to the caliphate and provided justification for future expansion north into the land of the kâfirs. Adopting the conceptual view of a deep and permeable borderlands where the ethnic and religious diversity of the Ottoman Empire can be seen to stretch unbroken to the similarly diverse lands of neighboring Poland-Lithuania, new continuities in pre-modern Muslim European experiences emerge. While the encounter described in the Risâle-i Tatar-i Leh has no known equal in the historical record, it shows that the Muslim communities as distant and seemingly disparate as Istanbul and the northern reaches of Lithuania were not far from one another’s thoughts. The Lipka Tatar/Ottoman Ulema co-authorship of the text allowed for novel comparisons of sacral architecture, religious education and training, linguistic practice, ethno-racial identity, and the Weltanschauung of two communities rooted in different and distant portions of the deep Abrahamic borderlands. These comparisons show us the breadth of religious practices in the early modern Islamic world and the modes by which distant Muslim communities employed their own knowledge of history, identity, and religious practice to forge reinforce new bonds of fraternity.