From Sahih Muslim (Hadith 6230):
A'isha reported that Allah's Messenger (may peace he upon him) lay on bed during one night and said:Were there a pious person from amongst my companions who should keep a watch for me during the nightt? She said: We heard the noise of arms, whereupon Allah's Messenger (ﷺ) said: Who is it? And Sa'd b. Abi Waqqas said: Allah's MesseDger. I have come to serve as your sentinel. 'A'isha said: Allah' s Messenger (ﷺ) slept (such a sound sleep) that I heard the noise of his snoring
Reference: Muslim 6230