It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "There will be a trial (fitnah) in which a man will be a believer in the morning and a disbeliever by the evening, except the one whom Allah keeps alive through knowledge."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7879