And how do you know that time had no beginning?
Prove it.
By which definition? If all you mean is 'for all time', then this is trivial. If you mean that time is infinite in extent, then you need to prove it.
But there are very good theoretical reasons to believe it may have had a beginning. The point is that we do not know, but you are rejecting one of the open possibilities for no good reason.
I agree. That is not what happened (no 'from'), even if time is finite.
The way to resolve this, is to stop thinking in terms of only space-time, which is the nature of our material universe. Rather, also think in terms of a realm where space and time are not connected, or where time and space can each act as independent variables.
If you could move space independent of time, you would be omnipresent. This is a classic attribute of God. If you could move in time independent of space, you would know how the entire universe changes in time. This is the classic attribute of God called omniscience. These two classic God references are not possible in space-time, since space and time have to work together, as one. This two legged race places limits connected to the speed of light. We can only be at one place at a time and we can only know the past.
Photons of light, which are part of space-time, have connected wavelength and frequency; connected via space-time. In a realm where space and time are not connected, each of these two photon variables could also act, independently. We would have wavelength without frequency, and frequency without wavelength. We would have the two parts needed to make photons and therefore energy. But since they are not connected; permanently, this realm could exist, before energy was in the universe. Independent space and time would first need to meet at a point junction and merge, so energy wavelength could connect to frequency to form energy, then the primordial atom could appear; connected space-time appears and there is light.
The proof of the possibility of a realm where time and space are not connected lies within the human imagination. The frontal lobe of the brain; moist evolve part of the brain, can process information in ways that are very similar to space and time not connected. This an experiment that anyone can do. This type of data processing suggests time without space and space without time is an information type realm connected to consciousness.
As an example, I can imagine a bridge built of nothing but el dente' spaghetti, that is 1 kilometer long. This is not possible in space-time, since the laws of physics, connected to space-time would not allow this. Gravity would cause the bridge to sag and shear. However, it would be possible, if I assembled the bridge in space independent of time. With time stopped, the force of gravity could not act, and the bridge would remain. I have not built this imaginary bridge in space-time. But the imagination can plan in a way where space and time do not have to be connected by the laws of physics. I can plan a week's vacation in my mind, in an hour, because space-time does not control information. It only applies to energy, substance; matter.
Our universe is not just space-time, but it also is impacted by the realm where space and time are not connected. This is easiest to see at the quantum level; synchronized particle pairs. This is similar to small scale omnipresent affect. This other realm can also can be understood, as part of our everyday life. For example, all the forces of nature are accelerations, with the units of acceleration, d/t/t. These units amount to space-time plus some independent time. This is not the classic way to look at acceleration and force, but it allows one to interface the quantum and inertial worlds as well as space before time and time before space. Now we can make the primordial atom from what appears to be nothing; in the imagination of God.
Space-time could use an update also. We model the universe as 4-D, with three spatial coordinates and one time coordinate. However, time is expressed in 4-D; (t0, t1, t2, t3). Time0 is a point in time. Time1 is a time line like velocity; d/t. Time2 is a time plane; acceleration; d/t/t, while Time3 is a time sphere or an acceleration of an acceleration; d/t/t/t. D/t/t/t is the accelerated expansion of our gravity force universe. Time in 4-D, offers a way to define each unique place in time within space-time. This is all controlled by time independent of space; laws of physics are the same in all references.