It is narrated from Sayyiduna Safwan bin Assal (may Allah be pleased with him), who said: The Messenger of Allah (peace and blessings be upon him) urged (people) to seek knowledge before it is taken away (disappears). A man said: How can it be taken away when we have learned it and taught it to our children? At this he (peace and blessings be upon him) became angry and said: "Are the Torah and the Injil not in the hands of the People of the Book? Then are they of any benefit to them?"
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7367