Praise be to Allah.
Many scholars are of the view that semen is pure (taahir), whether it is emitted as the result of a wet dream or intercourse. This is based on a great deal of evidence, including that which was narrated by Muslim in his Saheeh (288) from ‘Aa’ishah (may Allaah be pleased with her) who said: I remember scratching it [semen] from the garment of the Messenger of Allaah (peace and blessings of Allaah be upon him), then he prayed in it.
Al-Nawawi (may Allaah have mercy on him) said in Sharh Muslim (3/198): Many are of the view that semen is taahir (pure).
This was narrated from ‘Ali ibn Abi Taalib, Sa’d ibn Abi Waqqaas, Ibn ‘Umar, ‘Aa’ishah, Dawood and Ahmad according to one of the two reports. It is also the view of al-Shaafa’i and ashaab al-hadeeth. End quote. See Fath al-Baari (2/332).
It says in Fataawa al-Lajnah al-Daa’imah (5/381): The emission of semen as the result of a wet dream and the like does not make naajis the clothes worn by the one who has the dream, even if it gets on them, because semen is taahir. But it is prescribed to remove that which gets onto one’s clothes as a matter of cleanliness and removing dirt. End quote.
As for madhiy (prostatic fluid), which is what is emitted during foreplay or when thinking about intercourse, it is naajis, but sprinkling water on it is sufficient to purify it, because of the report narrated by Abu Dawood in his Sunan (210) and by al-Tirmidhi (115) and Ibn Majaah (506) from Sahl ibn Hunayf who said: I used to suffer from a great deal of madhiy, and I took many baths because of that. I asked the Messenger of Allaah (S) about that, and he said, “Wudoo’ is sufficient for you in this case.” I said, O Messenger of Allaah, what about the madhiy that gets onto my clothes? He said, “It is sufficient for you to pour a handful of water on the part of your clothes where you see the madhiy has gotten onto them.”
See also question no. 2458.
Based on this, intercourse and emission of semen does not mean that the clothes or body become naajis. As for madhiy, it is naajis but sharee’ah makes it easy to purify it, since sprinkling it with water is sufficient and it does not have to be washed.
The place that should be sprinkled with water is only the place where the madhiy got onto. As for the rest of the garment that was not touched by anything, it is taahir.
And Allaah knows best.