I am not claiming that there is no truth outside of Scripture but that it contains all that is necessary.
I am also aware that Augustine viewed toral tradition favourably such as:
(Letter 54 to Januarius, Chapter 1, Paragraph 1)
newadvent.org/fathers/1102054.htm
If you read the rest of the letter though you see he is dealing with things like customary practices and not doctrine.
However Augustine also said that things not found in Scripture could be believed or not. They are optional.
(Letter 147, To Paulina), Fathers of the Church Volume 20, The Catholic University of America Press, 1953, pp 170 & 173
I can’t provide a link to the above as I took it from the e-book.
In another work he gives purgatory *** an example of something that is optional for belief,.
(The Enchiridion Chapter 69)
newadvent.org/fathers/1302.htm