This article presents the Responsio in quaestione de muliere sarracena transeunte ad statum et ritum iudaicum (1451) by Alonso Fernández de Madrigal, “El Tostado” (1410–55), as a rich source for the study of conversion across minority groups. A trial conducted before the archbishop of Toledo concerning a Muslim woman turned Jew by her lover in Talavera de la Reina (Spain) caused a scandal in Christian society. As one of the most outstanding legal scholars at the University of Salamanca, Madrigal established the right of the archbishop of Toledo to judge an issue involving the two minorities and decided in favor of the woman returning to her faith of origin, instead of imposing the death penalty. While conversion superseded issues of illicit sexual relations, gender acted as a mitigating circumstance. This article will also consider how the three communities contributed to the survival of “cohabitation,” defined by Madrigal as social peace, and the preservation of the status of the different religions living together in Castile.