Sahih Muslim
The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) (Kitab Al-Fadail Al-Sahabah)
Book Number: 031 / Hadith Number: 5994
'A'isha reported that Allah's Messenger (may peace be upon him) said to her: Gabriel offered you greetings and I said: So there should be peace and mercy of Allah upon him.