I have heard that on one occasion, the Blessed One was staying at Uruvelā on the bank of the Nerañjarā River at the root of the Bodhi tree — the tree of awakening — newly awakened. And on that occasion he sat at the root of the Bodhi tree for seven days in one session, sensitive to the bliss of release. Then, with the passing of seven days, after emerging from that concentration, in the third watch of the night, he gave close attention to dependent co-arising in forward and reverse order, thus:

When this is, that is.
From the arising of this comes the arising of that.
When this isn't, that isn't.
From the cessation of this comes the cessation of that.

In other words:

From ignorance as a requisite condition come fabrications.
From fabrications as a requisite condition comes consciousness.
From consciousness as a requisite condition comes name-&-form.
From name-&-form as a requisite condition come the six sense media.
From the six sense media as a requisite condition comes contact.
From contact as a requisite condition comes feeling.
From feeling as a requisite condition comes craving.
From craving as a requisite condition comes clinging/sustenance.
From clinging/sustenance as a requisite condition comes becoming.
From becoming as a requisite condition comes birth.
From birth as a requisite condition, then aging-&-death, sorrow, lamentation, pain, distress, and despair come into play. Such is the origination of this entire mass of suffering & stress.
Now from the remainderless fading and cessation of that very ignorance comes the cessation of fabrications. From the cessation of fabrications comes the cessation of consciousness. From the cessation of consciousness comes the cessation of name-&-form. From the cessation of name-&-form comes the cessation of the six sense media. From the cessation of the six sense media comes the cessation of contact. From the cessation of contact comes the cessation of feeling. From the cessation of feeling comes the cessation of craving. From the cessation of craving comes the cessation of clinging/ sustenance. From the cessation of clinging/sustenance comes the cessation of becoming. From the cessation of becoming comes the cessation of birth. From the cessation of birth, then aging-&-death, sorrow, lamentation, pain, distress, and despair all cease. Such is the cessation of this entire mass of suffering & stress.

Then, on realizing the significance of that, the Blessed One on that occasion exclaimed: