If we reflect back into the past history of cosmos and ask “where did Brahman come from”, indulging in Upanishads (independent spiritual treatises) we would get our answer.
We must bear in mind that Brahman exists from the beginning of time; it neither has a beginning nor an end. God Almighty, creator of present cosmos is called Brahman in Hinduism.
Indulging in spiritual precepts of Hinduism we find that the present cosmos came into being when Brahman exploded self with a big bang. This happened when dissolution of old cosmos occurred.
At the time of occurrence of dissolution of old cosmos, the whole cosmos becomes a massive black hole finally reducing to the size of half a thumb. This half a thumb, the magnanimous primordial cosmic energy we called Brahman unable to contain itself for long in its prime pure state again explodes with a big bang and results in origin of a new cosmos.
Brahman exists from beginning of time yet cosmos after cosmos keep forming and dissolving, the dissolution of cosmos occurs via a massive black hole.
Brahman existing from times immemorial, from the beginning of time does not sustain any logical explanation, prime reason why analogy relating to origin of Brahman can be understood only through doctrine of Advaita Vedanta and doctrine of Maya propagated by Adi Shankaracharya.
As per philosophy of Advaita Vedanta, Brahman was the only truth of life. Other than Brahman nothing existed in cosmos. If we look at the boundary of cosmos, it does not seem to exist. If it at all existed, then what beyond! The present cosmos seems to exist only in thoughts of God Almighty was the summation of Adi Shankaracharya similar as existence of an image in a mirror.
Furthermore everything in cosmos if broken down to basic building block of cosmos, atoms and molecules then everything physical we see through our senses was but a gaseous formation, clusters of atoms and molecules, nothing more. If the absolute reality is so, then definitely whole world could exist only in thoughts of God Almighty. This is what doctrine of Maya (veil of illusion) is all about. Precepts of spirituality are well detailed in Hinduism, the oldest religion of world.
It is now confirmed that Brahman (God Almighty) did not originate, it all the time existed. What does originate is a cosmos.