Reformed (Presbyterian) apologist, Matt Slick, president of the Christian Apologetics Research Ministry (CARM) writes the following:
The Bible clearly tells us that it is the standard of truth. We are not to exceed what the Scriptures say. "Now these things, brethren, I have figuratively applied to myself and Apollos for your sakes, that in us you might learn not to exceed what is written, in order that no one of you might become arrogant in behalf of one against the other." (1 Cor. 4:6). (Matt Slick, “Is the Bible Alone Sufficient for Spiritual Truth?” URL: http://carm.org/bible-alone-sufficient-spiritual-truth)
There are a number of problems with this claim by Slick—
Firstly, not all 66 books of the Protestant canon had been inscripturated when Paul wrote 1 Cor 4:6. For Sola Scriptura to be true there must be Tota Scriptura. To cite this verse as “proof” of sola scriptura proves too much. If it teaches formal sufficiency, it teaches formal sufficiency of all scripture inscriptured up to, and including, 1 Cor 4:6, but no more.
Secondly, as most Protestant apologists admit (e.g. David T. King; Keith Mathison; James White), Paul taught oral tradition that was “God-breathed” revelation (cf. 2 Tim 3:16) but had not yet been inscriptured (1 Thess 2:13; 2 Thess 2:15; cf. 1 Cor 11:23ff; 15:3). One cannot conclude that the phrase, “to exceed what is written” teaches formal sufficiency of inscriptured revelation.
Thirdly, while much has been written on the phrase, the best suggestion is that the phrase refers to the Old Testament texts Paul had previously quoted:
1 Cor 1:19 (Isa 29:14)
1 Cor 1:31 (Jer 9:23)
1 Cor 2:9 (Isa 64:3)
1 Cor 2:16 (Isa 40:13)
1 Cor 3:19 (Job 5:13)
1 Cor 3:20 (Psa 94:11)
1 Cor 4:5 (while not an OT reference, alludes to a saying of Jesus which Paul may have access to in oral form [cf. Luke 12:1-3])
There is nothing in 1 Cor 4:6 that, exegetically, hints at sola scriptura.