Infant communion once treated as apostolic — later abrogated by Rome herself
Still stronger: for many ages, especially in the Roman and African churches, infants received the Eucharist as soon as they were baptized, and it was held necessary to their salvation.
Witnesses: Cyprian On the Lapsed; Innocent I to Milevis; Gelasius to the Picene bishops; Augustine in many places — not as a private whim but as the common Church view descending from apostolic tradition, and used as conceded ground against the Pelagians.
No contemporary writer objects. Roman doctors admit it: Vasquez and Maldonatus note Augustine's and Innocent's view held about six hundred years.
Yet Rome long ago abolished the custom, and Trent condemned it.
If unwritten traditions were already so uncertain and various in the first Christian centuries — and often deceived even good doctors — what certainty can sixteen later centuries add?
How unsafe, then, to take them as a rule of faith and set them equal in authority with sacred Scripture.
Latin
XXXVIII. Imo olim inter Christianos, praesertim in Ecclesia Romana atque Africana, & quidem per multa saecula, obtinuit consuetudo infantibus praebendi sacram Eucharistiam statim atque baptizati essent: istudque ad eorum salutem necessarium existimabatur, ut patet ex Cypriano lib. de lapsis num. 20. ex Innocentio primo Episcopo Romano in epist. ad Concil. Milevit. Item ex Gelasio Episcopo quoque Romano, in epist. ad omnes Episcopos per Picenum, & ex Augustino pluribus in locis. Qui sententiam istam de necessitate sacrae Eucharistiae respectu infantium non simpliciter probant, sed illam proferunt tanquam totius Ecclesiae sui temporis communem, adeoque ex Apostolica traditione descendentem, & inde tanquam ex re nota atque concessa argumenta ducunt adversus Pelagianos, ut speciatim videre est apud Augustinum libro 1. de peccati meritis & remissione cap. 24. & lib. 1. contra Julianum cap. 2. Nec est ullus scriptorum istius aevi qui reclamet. Idque agnoscunt ipsi Doctores Pontificii, ut Vasquez tom. 3. in 3. Thom. disp. 212. cap. 2. & Maldonat. in Joan. 6. num. 116. ubi dicit sententiam illam Augustini & Innocentii sexcentos circiter annos in Ecclesia viguisse. Et tamen haec consuetudo in Ecclesia Romana pridem abrogata est, sic a concilio Tridentino damnata. Si igitur jam olim primis post Christum temporibus traditiones non scriptae tam incertae & variae erant inter ipsos fideles & Doctores Ecclesiae, qui saepe traditionum obtentu decepti sunt, quid jam amplius certi post saecula sexdecim ex traditionibus haberi posse existimabimus? Et quam intutum atque periculosum erit illas assumere pro fidei regula, & ipsis Scripturis sacris authoritate aequare.