Lal said: “However, there is at least one sutta that says as long as true Dhamma will not totally disappear and there will be people who will be able to attain Nibbana. I hope someone may remember the name of that sutta and post it.”
I found this: MIL 5.1.7
… “The good law will now, Ānanda, endure for five hundred years.” In so saying he was fixing a limit to religion. But when in speaking to Subhadda, and by way of proclaiming who were the true Samaṇas, he said: “But if, in this system, the brethren live the perfect life, then the world would not be bereft of Arahats“
There is a longer explanation about those two statements.