God was, is, and is to come.

God said to Moses "I AM who I AM." (Exodus 3:14)

The original word for "I AM" is הָיָה . It is pronounced haya.

I always imagined that the original word for "I AM" would be Jehovah because I had heard that Jehovah meant self-existing one, but the original word here is not Jehovah. Haya means to exist, breathes, etc... See Blue Letter Bible.
Yehovah (Jehovah) means existing one.

The other day I wrote that God is the same. He was, He is, and He is to come. John wrote that in the book of Revelation 1:4. In the letter to the Hebrews 13:8, it says that "Jesus Christ is the same yesterday, and today, and forever."

God existed, and he exists, and he will exist. That means he is the same yesterday, today, and forever.

Is it written in the Old Testament? I could not find it. But the Jewish people say that God is "who was, is, and is to come." It is in Siddur Sim Shalom. I was wondering where in the Old Testament it said so. But now that I know the meaning of הָיָה (haya), I think that it is in the Hebrew language itself that explains God is who he was, is, and is to come. Doesn't it look like the meaning of הָיָה (haya) explains in itself that God was, is, and is to come? I think so!