The Buddha explains how many aeons have passed and gone by with a simile of four disciples with a hundred-year lifespan each recollecting a hundred thousand aeons each day and still not being able to count them all.
Sāvatthiyaṁ viharati.
At Sāvatthi.
Atha kho sambahulā bhikkhū yena bhagavā tenupasaṅkamiṁsu; upasaṅkamitvā bhagavantaṁ abhivādetvā ekamantaṁ nisinnā kho te bhikkhū bhagavantaṁ etadavocuṁ: “kīvabahukā nu kho, bhante, kappā abbhatītā atikkantā”ti?
Then several bhikkhus approached the Blessed One. Having drawn near to him, they paid homage and sat down to one side. Sitting to one side, those bhikkhus said this to the Blessed One: “Venerable sir, how many |aeons::an aeon is the lifespan of a world system, a vast cosmic time span [kappa]| have passed and gone by?”
“Bahukā kho, bhikkhave, kappā abbhatītā atikkantā. Te na sukarā saṅkhātuṁ: ‘ettakā kappā iti vā, ettakāni kappasatāni iti vā, ettakāni kappasahassāni iti vā, ettakāni kappasatasahassāni iti vā’”ti.
“Many aeons, bhikkhus, have passed and gone by. It is not easy to count them as so many aeons, or so many hundreds of aeons, or so many thousands of aeons, or so many hundreds of thousands of aeons.”
“Sakkā pana, bhante, upamaṁ kātun”ti?
“Then, is it possible to give a simile, venerable sir?”
“Sakkā, bhikkhave”ti bhagavā avoca.
“It is possible, bhikkhus,” the Blessed One said.
“Idhassu, bhikkhave, cattāro sāvakā vassasatāyukā vassasatajīvino. Te divase divase kappasatasahassaṁ kappasatasahassaṁ anussareyyuṁ. Ananussaritāva, bhikkhave, tehi kappā assu, atha kho te cattāro sāvakā vassasatāyukā vassasatajīvino vassasatassa accayena kālaṁ kareyyuṁ. Evaṁ bahukā kho, bhikkhave, kappā abbhatītā atikkantā. Te na sukarā saṅkhātuṁ: ‘ettakā kappā iti vā, ettakāni kappasatāni iti vā, ettakāni kappasahassāni iti vā, ettakāni kappasatasahassāni iti vā’ti.
“Suppose, bhikkhus, there were four disciples here each with a life span of a hundred years, living a hundred years, and each day they were each to recollect a hundred thousand aeons. There would still be aeons not yet recollected by them when those four disciples each with a life span of a hundred years, living a hundred years, would pass away at the end of a hundred years. It is not easy to count them and say that they are so many aeons, or so many hundreds of aeons, or so many thousands of aeons, or so many hundreds of thousands of aeons.
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.
For what reason? Bhikkhus, this |cyclic existence::wandering from one state of existence to another, the cycle of birth and death, moving on continuously [saṁsāra]| is without a discoverable beginning. A first point is not evident of beings who, obstructed by |ignorance::fundamental unawareness or misunderstanding of the true nature of reality, not experientially understanding the four noble truths [avijjā]| and fettered by |craving::wanting, yearning, longing, attachment, lit. thirst [taṇha]|, run on and wander in this cycle of existence. For such a long time, bhikkhus, you have experienced |suffering::discomfort, unpleasantness, discontentment, dissatisfaction, stress, pain, disease, i.e. mild or intense suffering [dukkha]|, |agony::intense suffering, anguish [tibba]|, and |calamity::disaster [byasana]|, the |cemetery::charnel ground [kaṭasī]| has been filled up with your bones. Therefore, bhikkhus, it is enough |to become disenchanted::to become disillusioned [nibbindituṃ]|, |to become detached::to become dispassionate [virajjituṁ]| and |to become free from::to be liberated from [vimuccituṃ]| |all conditions::all formations, all activities, all fabrications [sabbasaṅkhāra]|.”
At Sāvatthi.
Then several bhikkhus approached the Blessed One. Having drawn near to him, they paid homage and sat down to one side. Sitting to one side, those bhikkhus said this to the Blessed One: “Venerable sir, how many |aeons::an aeon is the lifespan of a world system, a vast cosmic time span [kappa]| have passed and gone by?”
“Many aeons, bhikkhus, have passed and gone by. It is not easy to count them as so many aeons, or so many hundreds of aeons, or so many thousands of aeons, or so many hundreds of thousands of aeons.”
“Then, is it possible to give a simile, venerable sir?”
“It is possible, bhikkhus,” the Blessed One said.
“Suppose, bhikkhus, there were four disciples here each with a life span of a hundred years, living a hundred years, and each day they were each to recollect a hundred thousand aeons. There would still be aeons not yet recollected by them when those four disciples each with a life span of a hundred years, living a hundred years, would pass away at the end of a hundred years. It is not easy to count them and say that they are so many aeons, or so many hundreds of aeons, or so many thousands of aeons, or so many hundreds of thousands of aeons.
For what reason? Bhikkhus, this |cyclic existence::wandering from one state of existence to another, the cycle of birth and death, moving on continuously [saṁsāra]| is without a discoverable beginning. A first point is not evident of beings who, obstructed by |ignorance::fundamental unawareness or misunderstanding of the true nature of reality, not experientially understanding the four noble truths [avijjā]| and fettered by |craving::wanting, yearning, longing, attachment, lit. thirst [taṇha]|, run on and wander in this cycle of existence. For such a long time, bhikkhus, you have experienced |suffering::discomfort, unpleasantness, discontentment, dissatisfaction, stress, pain, disease, i.e. mild or intense suffering [dukkha]|, |agony::intense suffering, anguish [tibba]|, and |calamity::disaster [byasana]|, the |cemetery::charnel ground [kaṭasī]| has been filled up with your bones. Therefore, bhikkhus, it is enough |to become disenchanted::to become disillusioned [nibbindituṃ]|, |to become detached::to become dispassionate [virajjituṁ]| and |to become free from::to be liberated from [vimuccituṃ]| |all conditions::all formations, all activities, all fabrications [sabbasaṅkhāra]|.”
Sāvatthiyaṁ viharati.
Atha kho sambahulā bhikkhū yena bhagavā tenupasaṅkamiṁsu; upasaṅkamitvā bhagavantaṁ abhivādetvā ekamantaṁ nisinnā kho te bhikkhū bhagavantaṁ etadavocuṁ: “kīvabahukā nu kho, bhante, kappā abbhatītā atikkantā”ti?
“Bahukā kho, bhikkhave, kappā abbhatītā atikkantā. Te na sukarā saṅkhātuṁ: ‘ettakā kappā iti vā, ettakāni kappasatāni iti vā, ettakāni kappasahassāni iti vā, ettakāni kappasatasahassāni iti vā’”ti.
“Sakkā pana, bhante, upamaṁ kātun”ti?
“Sakkā, bhikkhave”ti bhagavā avoca.
“Idhassu, bhikkhave, cattāro sāvakā vassasatāyukā vassasatajīvino. Te divase divase kappasatasahassaṁ kappasatasahassaṁ anussareyyuṁ. Ananussaritāva, bhikkhave, tehi kappā assu, atha kho te cattāro sāvakā vassasatāyukā vassasatajīvino vassasatassa accayena kālaṁ kareyyuṁ. Evaṁ bahukā kho, bhikkhave, kappā abbhatītā atikkantā. Te na sukarā saṅkhātuṁ: ‘ettakā kappā iti vā, ettakāni kappasatāni iti vā, ettakāni kappasahassāni iti vā, ettakāni kappasatasahassāni iti vā’ti.
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.