Abu As-Samh said:
"I used to serve the Messenger of Allah (ﷺ) and when he wanted to perform Ghusl he said: 'Turn your back.' So I turned my back to him and concealed him." (ES)
English reference (ES): Vol. 1, Book 1, Hadith 225 (ES)
Arabic reference (ES): Book 1, Hadith 226 (ES)