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 ﷺ وأنا ألعب مع الغلمان، فسلم علينا، فبعثنى في حاجةٍ، فأبطأت على أمي. فلما جئت قالت: ما حبسك؟ فقلت: بعثنى رسول الله ﷺ لحاجة، قالت: ما حاجته؟ قلت: إنها سر.قالت: لا تخبرن بسر رسول الله ﷺ أحداً. قال أنس: والله لو حدثت به أحداً لحدثتك به يا ثابت. ((رواه مسلم، وروى البخارى بعضه مختصراً)).