On one occasion the Blessed One was staying near Savatthi in Jeta's Grove, Anathapindika's monastery. Then Ven. Maha Kassapa went to the Blessed One and on arrival, having bowed down to him, sat to one side. As he was sitting there he said to the Blessed One, "What is the cause, lord, what is the reason, why before there were fewer training rules and yet more monks established in final gnosis, whereas now there are more training rules and yet fewer monks established in final gnosis?"
"That's the way it is, Kassapa. When beings are degenerating and the true Dhamma is disappearing, there are more training rules and yet fewer monks established in final gnosis. There is no disappearance of the true Dhamma as long as a counterfeit of the true Dhamma has not arisen in the world, but there is the disappearance of the true Dhamma when a counterfeit of the true Dhamma has arisen in the world. Just as there is no disappearance of gold as long as a counterfeit of gold has not arisen in the world, but there is the disappearance of gold when a counterfeit of gold has arisen in the world, in the same way there is no disappearance of the true Dhamma as long as a counterfeit of the true Dhamma has not arisen in the world, but there is the disappearance of the true Dhamma when a counterfeit of the true Dhamma has arisen in the world.1
"It's not the earth property that makes the true Dhamma disappear. It's not the water property... the fire property... the wind property that makes the true Dhamma disappear.2 It's worthless people who arise right here [within the Sangha] who make the true Dhamma disappear. The true Dhamma doesn't disappear the way a boat sinks all at once.
"These five downward-leading qualities tend to the confusion and disappearance of the true Dhamma. Which five? There is the case where the monks, nuns, male lay followers, & female lay followers live without respect, without deference, for the Teacher. They live without respect, without deference, for the Dhamma... for the Sangha... for the Training... for concentration. These are the five downward-leading qualities that tend to the confusion and disappearance of the true Dhamma.
"But these five qualities tend to the stability, the non-confusion, the non-disappearance of the true Dhamma. Which five? There is the case where the monks, nuns, male lay followers, & female lay followers live with respect, with deference, for the Teacher. They live with respect, with deference, for the Dhamma... for the Sangha... for the Training... for concentration. These are the five qualities that tend to the stability, the non-confusion, the non-disappearance of the true Dhamma."
Notes
1. Gold, of course, does not go out of existence simply because there is counterfeit gold. What happens is that it goes out of use: People find that counterfeit gold is easier to use. An added implication of this statement may be that as long as there is only genuine gold, people will not doubt its authenticity. When there is both genuine and counterfeit gold, doubts will arise as to what is genuine — all gold becomes doubtful — and people will end up using whichever is easier or more to their liking.
2. The point here is that the true Dhamma will not disappear through natural disasters, such as landslides, floods, fires, or windstorms. For an account of how people in the time of the Buddha understood natural events in terms of the four properties, see MN 28.