Actually the Bible does say about silent prayer as 'speaking in your heart'.
Matthew 6:6 ESV / 124 helpful votes
But when you pray, go into your room and shut the door and pray to your Father who is in secret. And your Father who sees in secret will reward you.
As she continued praying before the Lord, Eli observed her mouth. Hannah was speaking in her heart; only her lips moved, and her voice was not heard. Therefore Eli took her to be a drunken woman.
Likewise the Spirit helps us in our weakness. For we do not know what to pray for as we ought, but the Spirit himself intercedes for us with groanings too deep for words. And he who searches hearts knows what is the mind of the Spirit, because the Spirit intercedes for the saints according to the will of God.
To the choirmaster. A Psalm of David. O Lord, you have searched me and known me! You know when I sit down and when I rise up; you discern my thoughts from afar. You search out my path and my lying down and are acquainted with all my ways. Even before a word is on my tongue, behold, O Lord, you know it altogether.
The Lord will fight for you, and you have only to be silent.”
Mark 1:35 ESV / 18 helpful votes
And rising very early in the morning, while it was still dark, he departed and went out to a desolate place, and there he prayed.
Pray without ceasing,
A Psalm of David. The Lord is my shepherd; I shall not want. He makes me lie down in green pastures. He leads me beside still waters. He restores my soul. He leads me in paths of righteousness for his name's sake. Even though I walk through the valley of the shadow of death, I will fear no evil, for you are with me; your rod and your staff, they comfort me. You prepare a table before me in the presence of my enemies; you anoint my head with oil; my cup overflows. ...
Whoever keeps his mouth and his tongue keeps himself out of trouble.
Psalm 141:3 ESV / 12 helpful votes
Set a guard, O Lord, over my mouth; keep watch over the door of my lips!
James 5:13 ESV / 11 helpful votes
Is anyone among you suffering? Let him pray. Is anyone cheerful? Let him sing praise.
But the Lord is in his holy temple; let all the earth keep silence before him.”
Even a fool who keeps silent is considered wise; when he closes his lips, he is deemed intelligent.
A tonne of scripture is here! Sorry I just copied and pasted from the closest Bible website.
Paul told women to keep silent in church, why, so the women could LISTEN. How could anyone hear what God has to say when they are talking over Him all the time.