Hadith 501030
Chapter 2: Purity - كتاب الطهارة
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، وَعُثْمَانَ بْنَ عَفَّانَ، وَعَائِشَةَ، زَوْجَ النَّبِيِّ صلى الله عليه وسلم كَانُوا يَقُولُونَ إِذَا مَسَّ الْخِتَانُ الْخِتَانَ فَقَدْ وَجَبَ الْغُسْلُ .
Yahya related to me from Malik from Ibn Shihab from Said ibn al- Musayyab that Umar ibn al-Khattab and Uthman ibn Affan and A'isha, the wife of the Prophet, may Allah bless him and grant him peace, used to say, "When the circumcised part touches the circumcised part, ghusl is obligatory."
Reference Muwatta Malik 501030
USC-MSA web (English) reference : Book 2, Hadith 73