Narrated 'Aishah:
"The Messenger of Allah (ﷺ) did not sleep one night upon arriving in Al-Madinah. So he said: 'If only a righteous man would guard me tonight.'" She said: "So we were like that, when we heard the clanging of weapons. He said: 'Who is this?' So he said: 'Sa'd bin Abi Waqqas.' So the Messenger of Allah (ﷺ) said: 'What has brought you?' Sa'd said: 'Fear for the Messenger of Allah (ﷺ) came upon me, so I came to protect him.' So the Messenger of Allah (ﷺ) supplicated for him, then slept." (ES)
English reference (ES): Vol. 1, Book 46, Hadith 3756 (ES)
Arabic reference (ES): Book 49, Hadith 4122 (ES)