Musannaf Ibn Abi Shayba 27:514

Yazid ibn Harun narrated to us, from Yahya ibn Sa'id, that Abdullah informed him that Aisha used to narrate that the Messenger of Allah (peace and blessings of Allah be upon him) stayed awake one night while he was beside me. She said: I said, "O Messenger of Allah, what is the matter with you?" He said, "I wish a righteous man from my Ummah would guard me tonight." She said: While we were like that, I heard the sound of weapons. The Messenger of Allah (peace and blessings of Allah be upon him) said, "Who is this?" He said, "I am Sa'd ibn Malik." He said, "What brought you?" I said, "I came to guard you, O Messenger of Allah." She said: Then I heard the snoring of the Messenger of Allah (peace and blessings of Allah be upon him) in his sleep.