Digha Nikaya 2:116
SUJATOIdha, bhikkhave, bhikkhu santaṁ vā ajjhattaṁ kāmacchandaṁ ‘atthi me ajjhattaṁ kāmacchando’ti pajānāti, asantaṁ vā ajjhattaṁ kāmacchandaṁ ‘natthi me ajjhattaṁ kāmacchando’ti pajānāti, yathā ca anuppannassa kāmacchandassa uppādo hoti tañca pajānāti, yathā ca uppannassa kāmacchandassa pahānaṁ hoti tañca pajānāti, yathā ca pahīnassa kāmacchandassa āyatiṁ anuppādo hoti tañca pajānāti.
It’s when a mendicant who has sensual desire in them understands: ‘I have sensual desire in me.’ When they don’t have sensual desire in them, they understand: ‘I don’t have sensual desire in me.’ They understand how sensual desire arises; how, when it’s already arisen, it’s given up; and how, once it’s given up, it doesn’t arise again in the future.