In the version of Muslim:

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

وَلِمُسْلِمٍ: { لَقَدْ كُنْتُ أَفْرُكُهُ مِنْ ثَوْبٍ رَسُولِ اَللَّهِ ‏- صلى الله عليه وسلم ‏-فَرْكًا, فَيُصَلِّي فِيهِ } [1]‏ .‏