Muwatta Malik, Book 5, Hadith 229 (In-Book)

Yahya related to me from Malik from Safwan ibn Sulaym from Ata ibn Yasar from Abu Said al-Khudri that the Messenger of Allah, may Allah bless him and grant him peace, said, "Ghusl on the day of jumua is incumbent on every male who has reached puberty."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ صَفْوَانَ بْنِ سُلَيْمٍ، عَنْ عَطَاءِ بْنِ يَسَارٍ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ غُسْلُ يَوْمِ الْجُمُعَةِ وَاجِبٌ عَلَى كُلِّ مُحْتَلِمٍ ‏" ‏ ‏.‏

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also referenced under: Book 5, Hadith 4 (USC-MSA)