Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says: The Prophet (peace and blessings be upon him) requested Sayyiduna Jibril (peace be upon him) that he wished to see him in his true form. He said: Supplicate to your Lord. So he supplicated to his Lord, and a blackness began to appear from the direction of the east, and it began to rise and spread. When the Prophet (peace and blessings be upon him) saw him, he fell unconscious. Sayyiduna Jibril (peace be upon him) came to him, covered him (peace and blessings be upon him), and began wiping the saliva from the corners of his mouth.
Imam Ahmad and al-Tabarani recorded it, and the narrators of both are thiqat (trustworthy).