Revelation would descend upon the Messenger of Allah (may Allah's peace and blessings be upon him) on a cold morning and his forehead would stream with perspiration
Authentic hadithعن عائشة رضي الله عنها ، قالت: «إنْ كانَ لَيَنْزِلُ على رسولِ اللهِ صلى الله عليه وسلم في الغَدَاةِ الباردةِ، ثم تَفِيضُ جَبْهَتُه عَرَقًا».
‘Ā'ishah (may Allah be pleased with her) reported: Revelation would descend upon the Messenger of Allah (may Allah's peace and blessings be upon him) on a cold morning and his forehead would stream with perspiration.'
Explanation
The Mother of the Believers ‘Ā'ishah (may Allah be pleased with her) says in this Hadīth that revelation would descend upon the Messenger of Allah (may Allah's peace and blessings be upon him) on a cold morning and his forehead would perspire so much, due to the difficulty of receiving revelation.
Source · Narrated by Muslim
From the Hadith Encyclopedia (hadeethenc.com).