Sahih Muslim 288a
Sahih Muslim · Book 2: The Book of Purification · The ruling on semen
Alqama and Aswad reported:
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى ، أَخْبَرَنَا خَالِدُ بْنُ عَبْدِ اللَّهِ ، عَنْ خَالِدٍ ، عَنْ أَبِي مَعْشَرٍ ، عَنْ إِبْرَاهِيمَ ، عَنْ عَلْقَمَةَ ، وَالأَسْوَدِ ، أَنَّ رَجُلاً، نَزَلَ بِعَائِشَةَ فَأَصْبَحَ يَغْسِلُ ثَوْبَهُ فَقَالَتْ عَائِشَةُ إِنَّمَا كَانَ يُجْزِئُكَ إِنْ رَأَيْتَهُ أَنْ تَغْسِلَ مَكَانَهُ فَإِنْ لَمْ تَرَ نَضَحْتَ حَوْلَهُ وَلَقَدْ رَأَيْتُنِي أَفْرُكُهُ مِنْ ثَوْبِ رَسُولِ اللَّهِ صلى الله عليه وسلم فَرْكًا فَيُصَلِّي فِيهِ .
A person stayed in the house of A'isha and in the morning began to wash his garment. A'isha said: In case you saw it (i. e. drop of semen), it would have served the purpose (of purifying the garment) if you had simply washed that spot; and in case you did not see it, it would have been enough to sprinkle water around it, for when I saw that on the garment of the Messenger of Allah (ﷺ). I simply scraped it off and he offered prayer, while putting that on.