Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: "People will continue to be upon good as long as knowledge reaches them from the Companions of the Messenger of Allah (peace and blessings be upon him) and from their elders; but when knowledge comes from their young ones, that will be the time of their destruction."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8557