At Sāvatthi.

"Bhikkhus, this cyclic existence is without a discoverable beginning. A first point is not discerned for beings who, obstructed by ignorance and fettered by craving, run on and wander in this cycle of existence.

Suppose, bhikkhus, a stick were thrown in the air. Sometimes it lands on its base, sometimes in the middle, and sometimes on its tip. In the same way, bhikkhus, beings obstructed by ignorance and fettered by craving, continue to run and wander in this cycle of existence. Sometimes they go from this world to the other world, and sometimes they come from the other world to this world.

For what reason? Bhikkhus, this cyclic existence is without a discoverable beginning. A first point is not discerned for beings who, obstructed by ignorance and fettered by craving, run on and wander in this cycle of existence. For such a long time, bhikkhus, you have experienced suffering, agony, and calamity, the cemetery has been filled up with your bones. Therefore, bhikkhus, it is enough to become disenchanted, to become detached and to become free from all conditions."