سنن النسائي

It was narrated that 'Aishah said: "I noticed that the Messenger of Allah (ﷺ) was not there one night, and I thought that he had gone to one of his other wives, so I reached out for him, and found him bowing or prostrating, and saying: 'Subhanaka wa bi hamdika la ilaha illa anta (Glory and praise be to You, there is none worthy of worship but You).' I said: 'May my father and mother be sacrificed for you; you were doing one thing, and I was thinking of something else.'"