Bulugh al-Maram, Book 1, Hadith 32 (In-Book)

In the version of Muslim: “I used to scrape it (the semen) off the garment of Allah’s Messenger and then he offered prayer with it.

وَلِمُسْلِمٍ: { لَقَدْ كُنْتُ أَفْرُكُهُ مِنْ ثَوْبٍ رَسُولِ اَللَّهِ ‏- صلى الله عليه وسلم ‏-فَرْكًا, فَيُصَلِّي فِيهِ } (37)‏.‏ ‏2 ‏- صحيح.‏ رواه مسلم (288)‏.‏

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also referenced under: Book 1, Hadith 31 (English)