Stephen prayed for his persecutors, who had not been able even to listen to the Name of Christ, when he said of those very men by whom he was being stoned: "Lord, lay not this sin to their charge" And we see the result of this prayer in the case of the Apostle, for Paul, who kept the garments of those who were stoning Stephen, not long after became an apostle by the grace of God, having before been a persecutor.
St. Ambrose “The Sacred Writings of St. Ambrose”, Jazzybee Verlag