Here are St. Augustine, St. Ambrose, and St. John Chrysostom speaking clearly against EVEN the explicit baptism of desire of the catechumen:
St Augustine, 395: “… God does not forgive sins except to the baptized.”
St. Augustine, 412: “… the Punic Christians call Baptism itself nothing else but salvation… Whence does this derive, except from an ancient and, as I suppose, apostolic tradition, by which the Churches of Christ hold inherently that without Baptism and participation at the table of the Lord it is impossible for any man to attain either to the Kingdom of God or to salvation and life eternal? This is the witness of Scripture, too.”
St. Augustine, 391: “When we shall have come into His [God’s] sight, we shall behold the equity of God’s justice. Then no one will say:… ‘Why was this man led by God’s direction to be baptized, while that man, though he lived properly as a catechumen, was killed in a sudden disaster, and was not baptized?’ Look for rewards, and you will find nothing except punishments.”
St. Augustine: “However much progress the catechumen should make, he still carries the load of his iniquity: nor is it removed from him unless he comes to Baptism.”
St. Augustine: “If you wish to be a Catholic, do not venture to believe, to say, or to teach that ‘ they whom the Lord has predestinated for baptism can be snatched away from his predestination, or die before that has been accomplished in them which the Almighty has predestined.’ There is in such a dogma more power than I can tell assigned to chances in opposition to the power of God, by the occurrence of which casualties that which He has predestinated is not permitted to come to pass. It is hardly necessary to spend time or earnest words in cautioning the man who takes up with this error against the absolute vortex of confusion into which it will absorb him, when I shall sufficiently meet the case if I briefly warn the prudent man who is ready to receive correction against the threatening mischief.” (On the Soul and Its Origin 3, 13)
St. Ambrose, De mysteriis, 390-391 A.D.:
“You have read, therefore, that the three witnesses in Baptism are one: water, blood, and the spirit; and if you withdraw any one of these, the Sacrament of Baptism is not valid. For what is water without the cross of Christ? A common element without any sacramental effect. Nor on the other hand is there any mystery of regeneration without water: for ‘unless a man be born again of water and the Spirit, he cannot enter the kingdom of God.’ [John 3:5] Even a catechumen believes in the cross of the Lord Jesus, by which also he is signed; but, unless he be baptized in the name of the Father and of the Son and of the Holy Spirit, he cannot receive the remission of sins nor be recipient of the gift of spiritual grace.”
St. Ambrose, The Duties of Clergy, 391 A.D.:
“The Church was redeemed at the price of Christ’s blood. Jew or Greek, it makes no difference; but if he has believed he must circumcise himself from his sins so that he can be saved;...for no one ascends into the kingdom of heaven except through the Sacrament of Baptism.”
St. Ambrose, The Duties of Clergy, 391 A.D.:
“Unless a man be born again of water and the Holy Spirit, he cannot enter the kingdom of God.’ No one excepted: not the infant, not the one prevented by some necessity.”
St. John Chrysostom, The Consolation of Death: “And well should the pagan lament, who not knowing God, dying goes straight to punishment. Well should the Jew mourn, who not believing in Christ, has assigned his soul to perdition.”
It should be noted that since the term “baptism of desire” was not in use at the time, one won’t find St. John Chrysostom or any other father explicitly rejecting that term. They reject baptism of desire when they reject the concept that unbaptized catechumens can be saved without Baptism, as St. John Chrysostom repeatedly does.
St. John Chrysostom, The Consolation of Death: “And plainly must we grieve for our own catechumens, should they, either through their own unbelief or through their own neglect, depart this life without the saving grace of baptism.”
St. John Chrysostom, Hom. in Io. 25, 3:
“For the Catechumen is a stranger to the Faithful… One has Christ for his King; the other sin and the devil; the food of one is Christ, of the other, that meat which decays and perishes… Since then we have nothing in common, in what, tell me, shall we hold communion?… Let us then give diligence that we may become citizens of the city above… for if it should come to pass (which God forbid!) that through the sudden arrival of death we depart hence uninitiated, though we have ten thousand virtues, our portion will be none other than hell, and the venomous worm, and fire unquenchable, and bonds indissoluble.”
St. John Chrysostom, Homily III. On Phil. 1:1-20:
“Weep for the unbelievers; weep for those who differ in nowise from them, those who depart hence without the illumination, without the seal! They indeed deserve our wailing, they deserve our groans; they are outside the Palace, with the culprits, with the condemned: for, ‘Verily I say unto you, Except a man be born again of water and the Spirit, he shall not enter into the kingdom of Heaven.”
The “seal” is the fathers’ term for the mark of the Sacrament of Baptism. And here we see St. John affirming the apostolic truth held by all the fathers: that no one – including a catechumen – is saved without being born again of water and the Spirit in the Sacrament of Baptism.
St. John Chrysostom, Homily XXV: “Hear, ye as many as are unilluminated, shudder, groan, fearful is the threat, fearful is the sentence. ‘It is not possible,’ He [Christ] saith, ‘for one not born of water and the Spirit to enter into the Kingdom of heaven’; because he wears the raiment of death, of cursing, of perdition, he hath not yet received his Lord’s token, he is a stranger and an alien, he hath not the royal watchword. ‘Except,’ He saith, ‘a man be born again of water and the Spirit, he cannot enter into the Kingdom of heaven.”
St. John Chrysostom clearly rejected any possibility of salvation for one who has not received the Sacrament of Baptism. He affirmed the words of Christ in John 3:5 with an unequivocally literal understanding, which is the unanimous teaching of Tradition and the teaching of defined Catholic dogma.