God is, by definition, that being from which everything else came but who Himself came from nothing else. In this regard, some have called God the causeless Cause. We say that everything must have a cause. However, if we apply this reasoning forever into the past, we must accept a logical requirement for one original cause that had no prior cause. This original cause must contain within itself the source of its own being. When we get back to this original causeless Cause, we have come to God.
Now, you did not ask for logical reasoning, but rather for scriptures, I do not want to disappoint you. Two requirements of this causeless Cause are eternal existence and self-existence. Let us look at each of these attributes of God and support them by scripture.
If God is the original cause of all things, then He must be before all other things. And, if He is to have no cause outside of Himself, then He must be eternal in His existence. Not only is there no time when God was not, but His very existence transcends time--He exists outside the dimension of time. This is precisely the God described in the Bible.
According to Psalm 90:2, God is God "from everlasting to everlasting." He is "from everlasting" (Psalm 93:2). Other beings may exist eternally into the future, but only God can exist eternally in the past. Nothing came before Him. He has no rivals. He says of Himself, "I am the first, and I am the last; and beside me there is no God" (Isaiah 44:6).
But more than that, God is not even limited to the framework of time. In Isaiah 57:15, He introduces Himself as "the high and lofty One that inhabiteth eternity, whose name is Holy." Notice that God inhabits or dwells in eternity. Though He certainly works in time, time does not bind Him as it does other things. He inhabits eternity. We cannot much understand this dimension called eternity and certainly do not fully grasp its meaning. It must suffice us to understand it according to its negative definition--it is not time bound or time directed as our present universe is. Therefore, we can be uplifted with words such as these: "The eternal God is thy refuge, and underneath are the everlasting arms" (Deuteronomy 33:27).
It used to be that you would hear someone described as a self-made man. This was a man who without external advantages "lifted himself up by his own bootstraps" and made something of himself. And, although this may describe a type of personality we can understand, there is really no such thing as a self-made man. Nothing can be the source of its own existence--unless, of course, that something is God.
To speak of the self-existence of God does not mean that He brought Himself into existence. Since God is from everlasting, this is not necessary. However, it does mean that God is the source of His own being. Everything else has its origin in something else and exists because that something brought it into existence. In a sense, God is His own original first cause. He did not come into being; He simply is. When Moses asked for a calling card, a letter of introduction so to speak, from God to the children of Israel, God replied, I AM THAT I AM: and he said, Thus shalt thou say unto the children of Israel, I AM hath sent me unto you" (Exodus 3:14). The verb, AM, is simply another form of "to be" (indicating the being of God) or "is." The question is not how God came into being because He is the great I AM. God by definition is that being who exists in and of Himself.
This self-existence is seen in other passages as well. According to John 5:26, "the Father hath life in himself." That is, the life of God comes from God. You and I cannot say that. No other being can say that. Self-existence is one of the unique characteristics of God. Of Him scripture declares, "Who only hath immortality" (1Timothy 6:16). Only God has full control over His own existence. Even when God came as the God- an in the form of Jesus Christ, He could not simply be killed. Of His life, Jesus testified, "I lay down my life, that I might take it again. No man taketh it from me, but I lay it down of myself. I have power to lay it down, and I have power to take it again" (John 10:17-18).
God powerfully proclaims His own existence in Deuteronomy 32:40 - " For I lift up my hand to heaven, and say, I live for ever." Coming from anyone other than God, this would be the ravings of a madman. From God, it is simply the truth. Seven times in the Bible, God declares Himself to be the first and the last (Isaiah 41:4; 44:6; 48:12; Revelation 1:11, 17; 2:8; 22:13). Nothing came before Him and nothing will exist beyond Him.
So, where did God come from? The best answer I can give is that God came from Himself.