Library Eusebius of Caesarea Church History
Book 7
Chapter 3: Cyprian, and the Bishops with him, first taught that it was necessary to purify by Baptism those converted from Heresy
First of all, Cyprian, pastor of the parish of Carthage, maintained that they should not be received except they had been purified from their error by baptism. But Stephen considering it unnecessary to add any innovation contrary to the tradition which had been held from the beginning, was very indignant at this.
English translation by Arthur Cushman McGiffert, in Nicene and Post-Nicene Fathers, Series II, Vol. I (eds. Philip Schaff and Henry Wace; Buffalo: Christian Literature Publishing Co., 1890). Public domain. Digital text via New Advent Church Fathers.