At one time the Buddha was staying near Sāvatthī. “Mendicants, this transmigration has no known beginning. No first point is found of sentient beings roaming and transmigrating, shrouded by ignorance and fettered by craving. When you see someone in a sorry state, in distress, you should conclude: ‘In all this long time, we too have undergone the same thing.’ Why is that? This transmigration has no known beginning. … This is quite enough for you to become disillusioned, dispassionate, and freed regarding all conditions.”

Linked Discourses 15.12 Chapter Two In a Good Way

At Sāvatthī. “Mendicants, this transmigration has no known beginning. … When you see someone in a good way, in a happy state, you should conclude: ‘In all this long time, we too have undergone the same thing.’ Why is that? This transmigration has no known beginning. … This is quite enough for you to become disillusioned, dispassionate, and freed regarding all conditions.”

Linked Discourses 15.13 Chapter Two Thirty Mendicants