It was narrated that 'Amr bin Maimun said:"I asked Sulaiman bin Yasar about a garment which gets semen on it. 'Should I wash it off or wash the entire garment?' Sulaiman said: 'Aishah said: "Semen used to get on the garment of the Messenger of Allah and he would wash it off his garment, then he would go out to pray wearing that garment, and I could see the marks left on it by washing."
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدَةُ بْنُ سُلَيْمَانَ، عَنْ عَمْرِو بْنِ مَيْمُونٍ، قَالَ سَأَلْتُ سُلَيْمَانَ بْنَ يَسَارٍ عَنِ الثَّوْبِ، يُصِيبُهُ الْمَنِيُّ أَنَغْسِلُهُ أَوْ نَغْسِلُ الثَّوْبَ كُلَّهُ قَالَ سُلَيْمَانُ قَالَتْ عَائِشَةُ كَانَ النَّبِيُّ ـ صلى الله عليه وسلم ـ يُصِيبُ ثَوْبَهُ فَيَغْسِلُهُ مِنْ ثَوْبِهِ ثُمَّ يَخْرُجُ فِي ثَوْبِهِ إِلَى الصَّلاَةِ وَأَنَا أَرَى أَثَرَ الْغُسْلِ فِيهِ .
IbnMaja
The Book of Purification and its Sunnah • Hadith 536