What does St. Augustine say about tradition?

In his treatment of the dispute over the validity of the baptism of the heretical Donatists, St. Augustine writes, “And this custom [i.e., the invalidity of their baptism], coming, I suppose, from apostolical tradition (like many other things which are held to have been handed down under their actual sanction, because they are preserved throughout the whole Church, though they are not found either in their letters, or in the Councils of their successors).”²⁵¹