Anas said, "I was serving the Messenger of Allah, may Allah blesshim and grant him peace, one day. When I thought I had finished servinghim, I said, 'The Prophet, may Allah bless him and grant him peace, ishaving a midday nap.' So I left him and there were some children playing.I stood looking at them and their game. The Prophet, may Allah bless himand grant him peace, came out, and came up to them and greeted them. Thenhe called me and sent me to get something he needed. He remained in theshade until I came back to him. I was late for my mother and she and heasked, 'What kept you?' I replied, The Prophet, may Allah bless him andgrant him peace, sent me for something he needed.' 'What was it?' she asked.I replied, 'It is a secret of the Prophet, may Allah bless him and granthim peace.' She said, Keep the secret of the Messenger of Allah, may Allahbless him and grant him peace.' I did not tell anyone that secret. If Ihad told it, I would have told it to her.'"
English reference: Book 47, Hadith 1154
Arabic reference: Book 1, Hadith 1154