Abu Thawr al-Huddani (may Allah have mercy on him) said: I was brought to Sayyiduna Hudhayfah and Sayyiduna Abu Mas'ud (may Allah be pleased with them both) in the mosque, and Sayyiduna Abu Mas'ud (may Allah be pleased with him) was saying: By Allah, I did not think that this tribulation would go beyond its initial state without even a cupping-vessel's measure of blood being shed in it. At this Sayyiduna Hudhayfah (may Allah be pleased with him) said: But I know that it will go beyond its initial state even though not a cupping-vessel's measure of blood is shed in it. A man will be a believer in the morning and become a disbeliever by evening, and be a believer in the evening and become a disbeliever by morning; his heart will be turned upside down and he will go into a state of disgrace. Today he will fight the tribulation, and tomorrow Allah will kill him. At this Sayyiduna Abu Mas'ud (may Allah be pleased with him) said: This is how the Messenger of Allah (peace and blessings be upon him) told us about the tribulation.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14775