The writer to the Hebrews says that God has spoken to us in the past through the Old Testament prophets
1 God, having in the past spoken to the fathers through the prophets at many times and in various ways, 2 has at the end of these days spoken to us by his Son, whom he appointed heir of all things, through whom also he made the worlds.
The Apostle Paul tells Timothy that it was God's breath (or spirit) that influenced the writers to write the Scriptures
16 Every Scripture is God-breathed and profitable for teaching, for reproof, for correction, and for instruction in righteousness, 17 that each person who belongs to God may be complete, thoroughly equipped for every good work.
The Apostle Peter confirms that it was God's Spirit that produced the Scriptures.
21 For no prophecy ever came by the will of man: but holy men of God spoke, being moved by the Holy Spirit.
God told Moses that he would put His Words in the mouth of a Special person.
18 I will raise them up a prophet from amongst their brothers, like you. I will put my words in his mouth, and he shall speak to them all that I shall command him.
Several Old Testament prophets make it clear that they are speaking under God's guidance.
3 the LORD’s word came to Ezekiel the priest, the son of Buzi, in the land of the Chaldeans by the river Chebar; and the LORD’s hand was there on him.
1 The LORD’s word that came to Micah the Morashtite in the days of Jotham, Ahaz, and Hezekiah, kings of Judah, which he saw concerning Samaria and Jerusalem.
(look at the Evidence - you decide website www.theevidence.org.uk to see why we can believe this claim. )