Which book states The wages of sin is death?

Paul used this statement in Romans chapter 6, but apparently not intending it in the context of punishment for sin. Here he talks at length about the meaning of death and the importance of baptism. In some way, Christians are baptised into the death of Jesus and are buried with him. Our old self (KJV: 'old man') is crucified with him, the old, sinful body destroyed. Just as Christ was raised up from the dead, we should also walk with him in the newness of life. The metaphorical death of baptism is the end of sin. Read in context, the famous line, 'the wages of sin is death' seems to refer to this baptismal death.

The spiritual death of the body of each Christian convert, that Paul described as occurring at the time of baptism, shows that he saw death as having many meanings, not limited to the end of a physical life on earth. Tertullian (Against Marcion) interpreted this as a reference to punishment, the modern understanding.