New to this thread but have to jump in on this question.
I will say "YES!;" but will also say it depends on your understanding of what is meant by "one." The earliest scripture I can find that relates to this is in Deut 6:4, called the "Shema."
4 “Hear, O Israel! The Lord is our God, the Lord is one!
Or in the Hebrew: Shema Yisrael, Adonai Elohenu, Adonai echad.
God is addressed 3 times. But the operative word here is "echad." One. If we look elsewhere in Books of Moses to see how he used that word, we find it is not used as an absolute singularity; rather, it is a composite unity. Consider this verse:
Genesis 2:24
For this reason a man shall leave his father and his mother, and be joined to his wife; and they shall become one [echad] flesh.
Clearly husband and wife are still 2 individual people, but Moses says they are one, echad.
Since our Lord quotes this verse as well, He also considers married couples as echad, a composite unity.
BTW: Hebrew does have a word for an absolute singularity: Yachad.
The Trinity is NOT just a New Testament doctrine.