He imagines intercourse until he ejaculates. What is the ruling?
Question

                Allaah is not too shy to tell the truth. What is the ruling on what happens to me – thinking about intercourse, which is followed by ejaculation of semen as the result of desire? This is because of repeatedly thinking, without touching the private part and without moving or speaking. I am afraid that I may have committed a major sin, and I have done this numerous times because thinking is easy and is provocative for me. It is difficult to avoid it in some situations but praise be to Allaah I do not let my gaze wander.
Praise be to Allah.
    What you are doing, by deliberately thinking about 
    intercourse and enjoying that, which leads to emission of semen, is a haraam 
    action from which you have to repent, as well as regretting what has 
    happened in the past and resolving not to do it again. 

    The Standing Committee for Issuing Fatwas was asked: Is it 
    permissible for a young single man to think about intercourse, i.e., to 
    imagine that he is having intercourse with his wife although he is not yet 
    married? 

    They replied: 

    It is not permissible for him to do that, because it is a 
    means that may lead to committing immoral actions and falling into evil and 
    immoral ways. End quote from Fataawa al-Lajnah al-Daa’imah, 26/345. 
They were also asked: A 
    man’s desire may be provoked and he may think about intercourse a great 
    deal, and emit semen. Does this come under the heading of masturbation? This 
    is one thing. If he thinks about intercourse so that he can ejaculate and 
    feel pleasure, does that also come under the heading of masturbation? We 
    hope that you can explain the Islamic point of view to us concerning this 
    matter. May Allaah reward you with good. 

    They replied: If a thought crosses a person’s mind and he 
    thinks of intercourse accidentally, then there is no sin on him, in sha 
    Allaah, because it is narrated in a saheeh hadeeth from Abu Hurayrah (may 
    Allaah be pleased with him) that the Prophet  (peace and blessings of 
    Allaah be upon him) said: “Allaah has forgiven my ummah for what crosses 
    their minds.” According to another report: “For what crosses their minds, so 
    long as they do not act upon it or speak of it.” 

    But the one who thinks and ejaculates with pleasure as the 
    result of thinking has to do ghusl, because the rulings on janaabah apply to 
    him in this case. But if he thinks about that deliberately from time to 
    time, that is not permissible, and it does not befit the attitude of the 
    Muslim and is contrary to chivalry and good character. The Muslim should 
    refrain from that and keep himself busy with things that will prevent the 
    provocation of his desire and will benefit him in both spiritual and worldly 
    terms. Deliberately provoking desires in ways that are not acceptable or 
    prescribed in sharee’ah is harmful to one's physical and mental health, and 
    there is the fear that it may lead to bad consequences.    
The matter is even worse 
    if he does that when Allaah has given him a wife and when the husband 
    becomes accustomed to this bad habit and allows his mind wander freely, then 
    his relationship with his wife and the tranquility and compassion that 
    Allaah has created between husband and wife will be in danger. End quote. 

    Fataawa al-Lajnah al-Daa’imah, 
    22/66 

    We ask Allaah to help you to give up this evil deed and to 
    bless you with chastity. 
And Allaah knows 
    best.