The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
36. (The beginninglessness of the world; recommends itself to reason and is seen (from Scripture).
The beginninglessness of the world recommends itself to reason. For if it had a beginning it would follow that, the world springing into existence without a cause, the released souls also would again enter into the circle of transmigratory existence; and further, as then there would exist no determining cause of the unequal dispensation of pleasure and pain, we should have to acquire in the doctrine of rewards and punishments being allotted, without reference to previous good or bad action. That the Lord is not the cause of the inequality, has already been remarked. Nor can Nescience by itself be the cause, and it is of a uniform nature. On the other hand, Nescience may be the cause of inequality, if it be considered as having regard to merit accruing from action produced by the mental impressions or wrath, hatred, and other afflicting passions 1. Without merit and demerit nobody can enter into existence, and again, without a body merit and demerit cannot be formed; so that--on the doctrine
of the world having a beginning-we are led into a logical see-saw. The opposite doctrine, on the other hand, explains all matters in a manner analogous to the case of the seed and sprout, so that no difficulty remains.--Moreover, the fact of the world being without a beginning, is seen in Sruti and Smriti. In the first place, we have the scriptural passage, 'Let me enter with this living Self (gîva), &c. (Kh. Up. VI, 3, 2). Here the circumstance of the embodied Self (the individual soul) being called, previously to creation, 'the living Self'--a name applying to it in so far as it is the sustaining principle of the prânas--shows that this phenomenal world is without a beginning. For if it had a beginning, the prânas would not exist before that beginning, and how then could the embodied Self be denoted, with reference to the time of the world's beginning, by a name which depends on the existence of those prânas. Nor can it be said that it is so designated with a view to its future relation to the prânas; it being a settled principle that a past relation, as being already existing, is of greater force than a mere future relation.--Moreover, we have the mantra, 'As the creator formerly devised (akalpayat) sun and moon (Ri. Samh. X, 190, 3), which intimates the existence of former Kalpas. Smriti also declares the world to be without a beginning, 'Neither its form is known here, nor its end, nor its beginning, nor its support' (Bha. Gî. XV, 3). And the Purâna also declares that there is no measure of the past and the future Kalpas.
360:1 Râgadveshamohâ râgadayas te ka purusham dukhâdibhih klisyantîti klesâs teshâm karmapravrittyanugunâs tâbhir âkshiptam dharmâdilaksbilakshanam karma tadapekshâvidyâ. Ân. Gi.