Jesus referred to the Old Testament as Scripture and quoted from it often. And we’re told, “All Scripture is inspired by God and is useful to teach us what is true and to make us realize what is wrong in our lives. It straightens us out and teaches us to do what is right. It is God’s way of preparing us in every way, fully equipped for every good thing God wants us to do” (2 Timothy 3:16,17 – New Living Translation).
For more evidence for the Bible being God’s Word to us, please see the article, “Why You Can Believe the Bible”. It provides historical and archaeological reasons for the Bible’s authenticity, and answers skeptics questions about it.