Riyad as-Salihin 687
Thabit (May Allah be pleased with him) reported:
Anas (May Allah be pleased with him) said: Messenger of Allah (ﷺ) came to me while I was playing with the boys. He greeted us and sent me on an errand. This delayed my return to my mother. When I came to her, she asked, "What detained you?" I said; "Messenger of Allah (ﷺ) sent me on an errand." She asked, "What was it?" I said, "It is a secret." My mother said; "Do not disclose to anyone the secret of Messenger of Allah (ﷺ)." Anas (May Allah be pleased with him) said to Thabit (May Allah be pleased with him): By Allah, were I to tell it to anyone I would have told you. [Muslim] .
وعن ثابت عن أنس، رضي الله عنه قال‏:‏ أتى على رسول الله صلى الله عليه وسلم وأنا ألعب مع الغلمان، فسلم علينا، فبعثنى في حاجةٍ، فأبطأت على أمي‏.‏ فلما جئت قالت‏:‏ ما حبسك‏؟‏ فقلت‏:‏ بعثنى رسول الله صلى الله عليه وسلم لحاجة، قالت‏:‏ ما حاجته‏؟‏ قلت‏:‏ إنها سر‏.‏قالت‏:‏ لا تخبرن بسر رسول الله صلى الله عليه وسلم أحداً‏.‏ قال أنس‏:‏ والله لو حدثت به أحداً لحدثتك به يا ثابت‏.‏ ‏(‏‏(‏رواه مسلم، وروى البخارى بعضه مختصراً‏)‏‏)‏‏.‏