The fact that it is Allah Who created the Big Bang and the entire universe and all of life does not (Allah is beyond that) stem from any lack of explanation or lack of finding an answer to what went before it. In that case, that would require an explanation only to what was before and that all life and the universe were random, yet there is no such randomness on Earth (surely Allah is beyond that).
The whole universe and the living things in it point to one thing. Examination of them reveals something very extraordinary. The equilibrium in the universe, the order on Earth, life, a single cell in a living thing or even a single atom all speak of the extraordinary features they possess. They all speak of an intelligence. They say that this intelligence is far superior to anything you can see or know. They indicate a sublime Power that creates worlds within worlds and indicates intelligence and splendor even inside the atom. And that conclusion leads us to the existence of Almighty Allah.
…those who remember Allah, standing, sitting and lying on their sides, and reflect on the creation of the heavens and the earth: “Our Lord, You have not created this for nothing. Glory be to You! So safeguard us from the punishment of the Fire.” (Surah Al ‘Imran, 191)
There is no need to go back to the beginnings of the universe to see that. A single cell, a single hair or even a single atom, are sufficient to see the existence and greatness of Allah and thus to believe. Of course the creation of the universe through the Big Bang is a major event, by means of which Allah reveals His might and sublime power.
The idea that “this is not part of science” is a nonsensical one. Science exists so we can investigate Allah’s creations. It enables us to see the greatness of the message they bear. It enables us to better comprehend the greatness and might of Allah.