Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: The Prophet (peace and blessings be upon him) asked Jibril (peace be upon him) to show himself to him in his real form. Jibril (peace be upon him) said: "Supplicate to your Lord." So he (peace and blessings be upon him) supplicated to his Lord, and a blackness appeared from the direction of the east, which kept rising and spreading. When the Prophet (peace and blessings be upon him) saw it, he fell unconscious. So Jibril (peace be upon him) came to him, supported him, and wiped the saliva from (the side of) his mouth.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10987