1Thus have I heard. On one occasion the Blessed One was dwelling at Sāvatthī in Jeta's Grove, Anāthapiṇḍika's Park. There the Blessed One addressed the bhikkhus thus: "Bhikkhus!"

"Venerable sir!" those bhikkhus replied. The Blessed One said this:

2"Bhikkhus, this saṁsara is without discoverable beginning. [n.254] Anamataggo ’yaṁ bhikkhave saṁsāro. Spk resolves ā into anu amatagga, explaining: "Even if it should be pursued by knowledge for a hundred or a thousand years, it would be with unthought-of beginning, with unknown beginning (vassasataṁ vassasahassaṁ ñāṇena anugantva pi amataggo aviditaggo). It wouldn’t be possible to know its beginning from here or from there; the meaning is that it is without a delimiting first or last point. Saṁsara is the uninterruptedly occurring succession of the aggregates, etc. (khandhādīnaṁ avicchinnappavattā paṭipāṭi)."
The BHS equivalent of anamatagga is anavarāgra (e.g., at Mvu I 34,7), "without lower or upper limit." For various explanations, see CPD, s.v. an-amat’-agga. A first point is not discerned of beings roaming and wandering on hindered by ignorance and fettered by craving. Suppose, bhikkhus, a man would cut up whatever grass, sticks, branches, and foliage there are in this Jambudīpa and collect them together into a single heap. Having done so, he would put them down, saying for each one: ‘This is my mother, this my mother's mother.’ The sequence of that man's mothers and grandmothers would not come to an end, yet the grass, wood, branches, and foliage in this Jambudīpa would be used up and exhausted. For what reason? Because, bhikkhus, this saṁsara is without discoverable beginning. A first point is not discerned of beings roaming and wandering on hindered by ignorance and fettered by craving. For such a long time, bhikkhus, you have experienced suffering, anguish, and disaster, and swelled the cemetery. It is enough to experience revulsion towards all formations, enough to become dispassionate towards them, enough to be liberated from them." sn.ii.179

1Evaṁ me sutaṁ—​ ekaṁ samayaṁ bhagavā sāvatthiyaṁ vihārati jetavane anāthapiṇḍikassa ārāme. Tatra kho bhagavā bhikkhū āmantesi: "bhikkhavo"ti.

"Bhadante"ti te bhikkhū bhagavato paccassosuṁ. Bhagavā etadavoca:

2"Anamataggoyaṁ, bhikkhave, saṁsāro. Pubbā koṭi na paññāyati avijjānīvaraṇānaṁ sattānaṁ taṇhāsaṁyojanānaṁ sandhāvataṁ saṁsarataṁ. Seyyathāpi, bhikkhave, puriso yaṁ imasmiṁ jambudīpe tiṇakaṭṭhasākhāpalāsaṁ taṁ chetvā ekajjhaṁ saṁharitvā caturaṅgulaṁ caturaṅgulaṁ ghaṭikaṁ katvā nikkhipeyya: ‘Ayaṁ me mātā, tassā me mātu ayaṁ mātā’ti, apariyādinnāva, bhikkhave, tassa purisassa mātumātaro assu, atha imasmiṁ jambudīpe tiṇakaṭṭhasākhāpalāsaṁ parikkhayaṁ pariyādānaṁ gaccheyya. Taṁ kissa hetu? Anamataggoyaṁ, bhikkhave, saṁsāro. Pubbā koṭi na paññāyati avijjānīvaraṇānaṁ sattānaṁ taṇhāsaṁyojanānaṁ sandhāvataṁ saṁsarataṁ. Evaṁ dīgharattaṁ vo, bhikkhave, dukkhaṁ paccanubhūtaṁ tibbaṁ paccanubhūtaṁ byasanaṁ paccanubhūtaṁ, kaṭasī vaḍḍhitā. Yāvañcidaṁ, bhikkhave, alameva sabbasaṅkhāresu nibbindituṁ alaṁ virajjituṁ alaṁ vimuccitun"ti.

Paṭhamaṁ.