Two Medieval writers wrote the following:
All truth is from God;
though all will not be known until God is glorified. But this begins here below
with the revelation of the Scriptures.[1]
Let us search for
wisdom, let us consult sacred Scripture itself, apart from which nothing can be
found, nothing said which is solid or certain.[2]
All that God has said
or promised in sacred Scripture can be found reaffirmed in the creed . . . as
for anything that it outside the rule of holy Scripture, belief in it may not
be demanded of a Catholic.[3]
The sources for the above are:
[1] Rabanus Maurus, De cleric. inst.,
III, 2; PL, 107, 379-80
[2] Rupert of Deutz, In Apoc.; PL,
169, 1085; cf. 1203, 1493
[3] Idem, De Omnipotentia Dei, 27; PL,
170, 477-8
As Congar noted about Medieval authors and
the (material) sufficiency of Scripture:
An unknown author at
the beginning of the twelfth century, according to Fr Barré a disciple of St
Anselm, composed the famous Tractatus de Assumptione which, under St
Augustine’s name, had a great influence on the development of the doctrine of
the Assumption of our Lady. Practically speaking he reduces this doctrinal
development to Scripture, by the way of Christian contemplation (ratio),
which reads into the facts a meaning that goes far beyond the facts themselves
(PL, 40, 1143-4). Medieval writers had no difficulty in finding
everything in Scripture, since their principles of exegesis provided them with
the necessary means. (Yves M.J. Congar, Tradition and Traditions: An
Historical and a Theological Essay [trans. Michael Naseby; London: Burns and Oates Ltd., 1966], 113, emphasis in bold added)
I am sure if Irenaeus or Athanasius said
the above, they would latch onto them and take this to “prove” sola scriptura
was the belief of early Christianity. However, just as with the background of
Medieval authors (see Congar’s survey on pp. 111-16), in context, they
do not support belief in the formal sufficiency of the Bible