William Perkins
William Perkins, in his 1626 work, A Case of Conscience, affirms the Comma Johanneum while setting forth a dialogue between the Church and the Apostle John.
The Church: How may we be resolved that Jesus of Nazareth, the son of Mary, was the Son of God, and the Messiah? He came but basely into the world?
John: This is that Jesus Christ, which came by water (sanctification signified by the legal washings) and blood (imputation of Christs righteousness, or the sprinkling of his blood) not by water only, but by water and blood (because Christ worketh both justification and sanctification together) and it is that spirit (a man’s own conscience inwardly purified) that beareth witness, for that spirit is truth: (that is, that the testimony of the spirit of adoption, certifying us, that we are the sons of God, is true.)
For, (that I may speak yet more plainly,) there are three which bear record in heaven, the Father, the Word, (the Son) and the Holy Ghost; and these three are one (namely in testimony). And there are three which bear record in earth, the Spirit, and the water, and blood: and these three agree in one.
Source: William Perkins, A Case of Conscience [read online]