Anguttara Nikaya 1:14
SUJATOKiñca, bhikkhave, atthavasaṁ paṭicca ‘byādhidhammomhi, byādhiṁ anatīto’ti abhiṇhaṁ paccavekkhitabbaṁ itthiyā vā purisena vā gahaṭṭhena vā pabbajitena vā?
What is the advantage of often reviewing this: ‘I am liable to get sick, I am not exempt from sickness’?