अंगुत्तर निकाय 1:10
SUJATOKiñca, bhikkhave, atthavasaṁ paṭicca ‘jarādhammomhi, jaraṁ anatīto’ti abhiṇhaṁ paccavekkhitabbaṁ itthiyā vā purisena vā gahaṭṭhena vā pabbajitena vā?
What is the advantage for a woman or a man, a layperson or a renunciate of often reviewing this: ‘I am liable to grow old, I am not exempt from old age’?