Anguttara Nikaya 1:18
SUJATOKiñca, bhikkhave, atthavasaṁ paṭicca ‘maraṇadhammomhi, maraṇaṁ anatīto’ti abhiṇhaṁ paccavekkhitabbaṁ itthiyā vā purisena vā gahaṭṭhena vā pabbajitena vā?
What is the advantage of often reviewing this: ‘I am liable to die, I am not exempt from death’?