Good Manners and Form (Al-Adab)
Bukhari :: Book 8 :: Volume 73 :: Hadith 220
Narrated 'Aisha:
(the wife the Prophet) Allah's Apostle said, "O Aisha! This is Gabriel sending his greetings to you." I said, "Peace, and Allah's Mercy be on him." 'Aisha added: The Prophet used to see things which we used not to see.