Is Semen impure?
Question

We have learned that man was created from “worthless water”, namely semen, and that this “water” is an impurity. So is man’s origin impure or what?
Praise be to Allah.Is semen pure?
The fact that man was created from “worthless water” is a fact that is stated in the Quran and is obvious from experience. Allah, may He be Exalted, says (interpretation of the meaning):
“Did We not create you from a worthless water (semen, etc.)?” [Al-Mursalat 77:20]
“So let man see from what he is created! He is created from a water gushing forth” [At-Tariq 86:5-6]
This gushing, worthless water is semen, and according to the more correct of the two scholarly opinions it is pure. 
Evidence for the purity of semen
The purity of semen is indicated by a great deal of evidence, including the following:

The report narrated by Muslim (288) from `Aishah (may Allah be pleased with her) who said: I remember scratching it (semen) from the garment of the Messenger of Allah (blessings and peace of Allah be upon) thoroughly, then he prayed in it. It is well-known that scratching is not sufficient to remove impurity, which indicates that it is pure. 
“Further proof may be found in the fact that this water is the origin of the sincere slaves of Allah, such as the Prophets, Siddiqs, martyrs and righteous people, and the wisdom of Allah, may He be Exalted, dictates that the origin of these righteous people cannot be impure.” (Ash-Sharh Al-Mumti‘, 1/388)

Does semen make clothes impure?
The scholars of the Standing Committee for Issuing Fatwas were asked: If maniy gets onto clothes, does it make them impure? 
They replied: “The basic principle concerning it is that it is pure and we do not know of any evidence to suggest that it is impure.” (Fatawa Al-Lajnah Ad-Da’imah, 6/416 )
Shaykh Al-Islam Ibn Taymiyah (may Allah have mercy on him) said: 
“With regard to semen, the correct view is that it is pure, as is the view of Ash-Shafi`i and Ahmad, according to the well-known report from him. It was also said that it is impure, but it is sufficient to scratch it, as is the view of Abu Hanifah and Ahmad, according to the other report. 
And it was said that it must be washed , as is the view of Malik. 
The first view is the correct one, because it is well-known that the Companions experienced wet dreams at the time of the Prophet (blessings and peace of Allah be upon him) and that semen would get onto the body and clothes of one of them, and this is something that affects everyone. If it were impure, then it would have been obligatory for the Prophet (blessings and peace of Allah be upon him) to instruct them to remove that from their bodies and clothes, as he instructed them to clean themselves after relieving themselves, and as he instructed the menstruating woman to wash the menstrual blood from her garment. In fact, the issue of getting semen on one’s body or clothes is far more common than the issue of menstrual blood getting onto the woman’s garment. It is well-known that no one narrated that the Prophet (blessings and peace of Allah be upon him) instructed any of the Companions to wash semen from his body or clothes; thus it is known for certain that this was not obligatory for them, and this is definitive to anyone who examines the matter.” (Majmu` Al-Fatawa, 21/604, 605)
And Allah knows best.