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.
Historia Ecclesiastica
Book VII, Chapter 3. Cyprian, and the Bishops with him, first taught that it was necessary to purify by Baptism those converted from Heresy
1 section
Eusebius of Caesarea
Trans. Arthur Cushman McGiffert, A Select Library of Nicene and Post-Nicene Fathers of the Christian Church, Second Series, Volume I, 1890. Public domain.