72 Likewise another Lucius of Ausafa said: "According to the motion of my mind and of the Holy Spirit, since there is one God, the Father of our Lord Jesus Christ, and one Christ, and one hope, one Spirit, one Church, there ought also to be only one baptism. And therefore I say, both that if anything has been set on foot or done among the heretics, that it ought to be rescinded; and also, that they who come out from among the heretics should be baptized in the Church."
73. Let it therefore be pronounced of no effect that they baptize, who hear the words of God and do them not, when they shall begin to pass from unrighteousness to righteousness, that is, from the sand to the rock. And if this is not done, because what there was in them of Christ was not violated by their unrighteousness, then let this also be understood in the case of heretics: for neither is there the same hope in the unrighteous, so long as they are on the sand, as there is in those who are upon the rock; and yet there is in both the same baptism, although as it is said that there is one hope, so also is it said that there is one baptism.
Source: On Baptism, Against the Donatists (New Advent)