Mishkat al-Masabih 3 Purification كتاب الطهارة 195

وَعَنْ سُلَيْمَانَ بْنِ يَسَارٍ قَالَ: سَأَلْتُ عَائِشَةَ عَنِ الْمَنِيِّ يُصِيبُ الثَّوْبَ فَقَالَتْ كُنْتُ أَغْسِلُهُ مِنْ ثَوْبِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَيَخْرُجُ إِلَى الصَّلَاةِ وَأَثَرُ الْغَسْلِ فِي ثَوْبه بقع المَاء

Sulaiman b. Yasir said that he asked ‘A’isha about the prostatic fluid which gets on to a garment, and she replied, “I used to wash it from the garment at God’s messenger, and he would go out to prayer with the mark of the washing on his garment.” (Bukhari and Muslim.)