“the Church, having received this preaching and this faith, although scattered throughout…”

the Church, having received this preaching and this faith, although scattered throughout the whole world, yet, as if occupying but one house, carefully preserves it. She also believes these points [of doctrine] just as if she had but one soul, and one and the same heart, and she proclaims them, and teaches them, and hands them down, with perfect harmony, as if she possessed only one mouth. For, although the languages of the world are dissimilar, yet the import of the tradition is one and the same. For the Churches which have been planted in Germany do not believe or hand down anything different, nor do those in Spain, nor those in Gaul, nor those in the East, nor those in Egypt, nor those in Libya

Irenaeus · Against Heresies · ANF I, Against Heresies, Book I, Chapter X, 2

The oldest surviving statement that the church teaches one thing everywhere, made by a bishop in Gaul who had been taught in Asia and was writing about churches he names by province. It is the argument the succession lists exist to support: not that the bishops agree because they are bishops, but that a faith handed down through them has come out the same in six countries that had no way of checking with one another.