The Prophet ﷺ was unable to sleep one night and said, "If only a righteous man from my companions would guard me tonight." Just then we heard the sound of weapons.He asked, "Who is this?"The man replied, "It is Saad, Messenger of Allah. I have come to guard you."The Prophet ﷺ then slept until we heard him snoring.
أرق النبي ﷺ ذات ليلة فقال: ليت رجل صالح من أصحابي يحرسني الليلة إذ سمعنا صوت السلاح قال: من هذا؟ قال: سعد يا رسول الله جئت أحرسك، فنام النبي ﷺ حتى سمعنا غطيطه.
Bukhari narrated it in the Book of Wishing (7231) and Muslim in the Book of Virtues (2410), both from the hadith of Sulayman bin Bilal, who said, Yahya bin Saeed narrated to me, I heard Abdullah bin Amir bin Rabia say, Ayesha said, and he mentioned it. The wording given is that of Bukhari.In the version of Muslim, the Messenger of Allah ﷺ said to him, "What brought you here?" He said, "I felt fear for the Messenger of Allah ﷺ in my heart, so I came to guard him." The Prophet ﷺ then prayed for him, and he fell asleep.Saad is the son of Abu Waqqas, as is made explicit in the other narrations.