This is as I heard from the Blessed One. At one time, the Blessed One was staying in the city of Uruvelā, on the bank of the river Nerañjarā at the foot of the Bodhi Tree, having just realised supreme enlightenment. There, the Blessed One was sitting cross legged for seven days straight, experiencing the peace of liberation.
At the end of those seven days, the Blessed One emerged from that concentration and in the first watch of the night he reflected on the cause and effect method in forward order as follows,
“Iti imasmiṃ sati idaṃ hoti, imassa uppādā idaṃ uppajjati. yadidaṃ, avijjā paccayā saṅkhārā. Saṅkhāra paccayā viññāṇaṁ. Viññāṇa paccayā nāmarūpaṁ. Nāma rūpa paccayā saḷāyatanaṁ. Saḷāyatana paccayā phasso. Phassa paccayā vedanā. Vedanā paccayā taṇhā. Taṇhā paccayā upādānaṁ. Upādāna paccayā bhavo. Bhava paccayā jāti. Jāti paccayā jarā maraṇaṁ soka parideva dukkha domanassupāyāsā sambhavanti. Evametassa kevalassa dukkhakhandassa samudayo hoti.
When the cause exists the relevant effect exists. With the arising of the cause the relevant effect arises. That is, depending on not knowing the four noble truths (ignorance), formation arises. Depending on formation, consciousness arises. Depending on consciousness, mentality and materiality arise. Depending on mentality and materiality, the six sense bases arise. Depending on the six sense bases, contact arises. Depending on contact, feeling arises. Depending on feeling, craving arises. Depending on craving, clinging arises. Depending on clinging, the arranging of kamma arises. Depending on the arranging of kamma, birth arises. Depending on birth, aging, death, sorrow, weeping, pain, sadness, and despair arise. This is the arising of the whole mass of suffering.
Then, the Blessed One who realised this cause and effect method as it really is spoke the following inspired verse,
The liberated one is energetic and meditates.
At the time he is established
in the aids to Enlightenment,
all his doubts vanish.
As a result, he realises
the cause and effect method fully.