As above down to:

“Friend Ānanda, what is the cause and reason for the decline of the true Dhamma? And what is the cause and reason for the nondecline of the true Dhamma?”…

“It is, friend, when these four establishments of mindfulness are not developed and cultivated that the true Dhamma declines. And it is when these four establishments of mindfulness are developed and cultivated that the true Dhamma does not decline.”