He put on ihraam then he decided not to do Hajj
Question

                If a person puts on ihraam for ‘Umrah or Hajj, then he cancels it, what does he have to do?
Praise be to Allah.If he puts on the izaar 
    (lower garment) and rida’ (upper garment), but he does not have the 
    intention of doing Hajj or ‘Umrah, and he does not recite the Talbiyah, then 
    he has the choice. If he wishes he may start Hajj or ‘Umrah, and if he 
    wishes he may not do so. There is no sin on him if he has already done Hajj 
    and ‘Umrah, but if he intended to start Hajj or ‘Umrah then he cannot cancel 
    that and change his mind, rather he must complete that for which he entered 
    ihraam, in the manner prescribed in Islam, because Allaah says 
    (interpretation of the meaning): 
“And perform properly 
    (i.e. all the ceremonies according to the ways of Prophet Muhammad), the 
    Hajj and ‘Umrah (i.e. the pilgrimage to Makkah) for Allaah”

    [al-Baqarah 2:196]

    Hence it should be clear to you that once the Muslim starts 
    Hajj or ‘Umrah with the appropriate intention, he does not have the right to 
    stop that, rather he must complete what he has started, because of the aayah 
    quoted above, unless he has made a condition in case something prevented him 
    from doing it. In that case he may exit ihraam, because when Dabaa’ah bint 
    al-Zubayr said to the Prophet  (peace and blessings of Allaah be upon 
    him), “O Messenger of Allaah, I want to do Hajj but I am not sure (I will be 
    able to do it?),” he said, “Go for Hajj but make the condition that you will 
    exit ihraam if you are prevented from doing it.” (Saheeh – agreed upon). 

    And Allaah is the Source of strength. May Allaah send 
    blessings and peace upon our Prophet Muhammad.