Muwatta Malik, Book 17, Hadith 589 (In-Book)

Yahya related to me from Malik from Ibn Shihab from Said ibn al- Musayyab and from Abu Salama ibn Abd ar-Rahman from Abu Hurayra that the Messenger of Allah, may Allah bless him and grant him peace,said, "There is a tax of a fifth on buried treasure."

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، وَعَنْ أَبِي سَلَمَةَ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ فِي الرِّكَازِ الْخُمُسُ ‏" ‏ ‏.‏

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also referenced under: Book 17, Hadith 9 (USC-MSA)