The word for "scripture" in the Greek text is (ἡ) γραφή, often occurring in the plural, (τῆς) γραφῆς, which literally means "writing(s)." The word occurs approximately 50 times in the New Testament (depending on the manuscript used it is 50 or 51) and it seems pretty clear to me from a word search that this almost exclusively refers to the Old Testament writings when used by New Testament authors.

The exception is 2 Peter 3:16, which says:

> And regard the patience of our Lord as salvation, just as also our
> dear brother Paul wrote to you, according to the wisdom given to him,
> speaking of these things in all his letters [(ἐπιστολαῖς, epistles)]. 
> Some things in these letters are hard to understand, things the ignorant 
> and unstable twist to their own destruction, as they also do to the rest 
> of the scriptures [(γραφὰς, writings)] (2 Peter 3:15-16, NET).

This verse clearly refers to Paul's writings as "scriptures." Everywhere else it refers to the Old Testament (or to specific passages from the Old Testament).