Praise be to Allah
Maniy (semen) is considered taahir & pure according to the most correct opinion among the scholars. The evidence for this is the report of ‘Aa’ishah (may Allaah be pleased with her) who said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) used to wash the maniy (from his clothes) then go out to pray wearing the same clothes, and I could see the spot where he had washed it.” (Agreed upon).
According to a report narrated by Muslim: “I used to rub it (semen) thoroughly from the garment of the Messenger of Allaah (peace and blessings of Allaah be upon him), then he would pray in it.” According to another version: “I would scratch it from his garment with my nail when it had become dry.”
It is proven that the Prophet (peace and blessings of Allaah be upon him) used to leave it without washing it when it was wet; it was sufficient just to wipe it with ‘ood (a kind of aromatic wood) or something similar, as was reported by Imaam Ahmad in his Musnad (6/243) from ‘Aa’ishah (may Allaah be pleased with her), who said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) used to remove maniy from his garment with a twig of adhkhar (a kind of tree), then pray in that garment, and he would rub it from his garment once it was dry, and would pray in the same garment.” Ibn Khuzaymah reported it in his Saheeh, and Shaykh al-Albaani classed it as hasan in al-Irwa’ (1/197).
According to Hanafi Mazhab, mani (semen) is impure.
On the other hand, Madhiy (urethral discharge) is naajis (impure), because of the hadeeth of ‘Ali ibn Abi Taalib (may Allaah be pleased with him) who said: “I was a man who used to experience a lot of urethral discharge, so I told Miqdaad to ask the Messenger of Allaah (peace and blessings of Allaah be upon him) about it. So he asked him, and he said: ‘It requires wudoo’.’” (Agreed upon; this version was narrated by al-Bukhaari).
Ibn Qudaamah said in al-Mughni (1/168), “Ibn al-Mundhir said: ‘The scholars agree that passing stools or urine, the emission of madhiy or passing wind are all things that invalidate tahaarah (purity) [i.e. they mean that wudoo’ must be renewed]’.
Hence, as maniy is deemed to be taahir, if it gets on a person’s clothes it does not make them impure, and if he prays in those clothes there is nothing wrong with that.
Ibn Qudaamah said in al-Mughni (1/763): “Even though we say it is taahir, it is better to rub it, but if one prays (in those clothes) without rubbing it, this is acceptable.”
In the case of madhiy, it is sufficient to sprinkle water on it, because of the difficulty of doing otherwise. The evidence for this is the hadeeth narrated by Abu Dawud in his Sunan from Sahl ibn Haneef, who said: “I used to experience a lot of urethral discharge, and I used to do ghusl a lot. I asked the Messenger of Allaah (peace and blessings of Allaah be upon him) about it and he said: ‘It is sufficient for you to do wudoo’ (to purify yourself) from that.’ I said, ‘O Messenger of Allaah, what about when it gets on my clothes?’ He said: ‘It is sufficient for you to take a handful of water and sprinkle it on your clothes wherever you think (the madhiy) is.’” (Reported by al-Tirmidhi. He said: This is a saheeh hasan hadeeth, and the only other hadeeth about madhiy that we know is the hadeeth of Muhammad ibn Ishaaq).
The author of Tuhfat al-Ahwadhi (1/373) said: “This may be taken to prove that if madhiy gets on one's clothes, it is sufficient to sprinkle water on it; one does not have to wash it.”
Accordingy to Ahnaaf mazhab, it is required to wash the affected and soiled part of the clothe three times to make it pure.
And Allaah knows best.