20 Paul of Bobba said: "I for my part am not moved if some fail to uphold the faith and truth of the Church, seeing that the apostle says 'For what if some did not believe? Shall their unbelief make the faith of God without effect? God forbid: yea let God be true, but every man a liar.' But if God be true, how can the truth of baptism be in the company of heretics, where God is not?"
21. To him we answer: What is God among the covetous? And yet baptism exists among them; and so also it exists among heretics. For they among whom God is, are the temple of God. "But what agreement has the temple of God with idols?" Further, Paul considers, and Cyprian agrees with him, that covetousness is idolatry; and Cyprian himself again associates with his colleagues, who were robbers, but yet baptized, with great reward of toleration.
Source: On Baptism, Against the Donatists (New Advent)