Peace,
The Trinity is found in the OT.
This is for Muslim, Jews, anyone who doubts the Trinity.
Read through the OT.
God is referred to as the LORD, the Lord God, and the Spirit of the Lord.
Obviously, the Spirit of the Lord is the Lord manifested as the Spirit.
Here is God the Holy Spirit.
When the prophets saw God, often they saw a man seated upon a throne.
Who is the image of God?
Who is God manifested in the image of a man?
Here is God the Son.
Who's voice is powerful and sounds like thunder?
He spoke from the sky and brought the plauhes upon Egypt and gave manna in the desert? He manifested His prescence on top of Mt. Sinai.
Here is God the Father.
If you want to believe in the Trinity, then you'll see this clearly.
Blessings