Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) reports this saying of the Prophet (peace and blessings be upon him): "If a person were to do a deed inside a solid (that is, closed on every side) rock which has no door and no window, his deed would still come out to people, whatever that deed may be."
Ahmad and Abu Ya'la recorded it, and the chain of both is hasan (good).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الزهد / 17679
Hadith Gradingمحدثین:إسنادہ حسن۔
Hadith Takhrij«اخرجه ابو يعلى فى المسند (1378) أخرجه احمد فى المسند (28/3) ، أخرجه مسند أحمد برقم: 10846»