When there is a conflict between fulfilling an oath and honouring one's parents
Question

                What is the ruling on breaking the oath when one is not able to fulfil it? What is the ruling if fulfilling the oath conflicts with honouring one's parents?.
Praise be to Allah.
    Firstly: 

    The oath that one swears and resolves to do must be fulfilled 
    by doing what one swore to do or refraining from what one swore to refrain 
    from. If he does not do that, then he must offer kafaarat yameen (expiation 
    for breaching an oath). Expiation for breaking an oath has been discussed in 
    detail in the answer to question number
    45676. 

    Secondly: 

    If fulfilling an oath conflicts with honouring one's parents, 
    then precedence must be given to honouring one's parents, and one must break 
    the oath and offer expiation, so long as there is no sin involved in doing 
    so. 

    Muslim (1650) narrated from Abu Hurayrah (may Allah be 
    pleased with him) that the Messenger of Allah (blessings and peace of Allah 
    be upon him) said: “Whoever swears an oath then sees that something else is 
    better than it, let him do that and offer expiation for his oath.” 

    Al-Nawawi said:  

    In these hadeeths there is evidence that if a person swears 
    to do something or not to do something, and breaking the oath is better than 
    fulfilling the oath, it is mustahabb for him to break it but he must offer 
    expiation. This is agreed upon. End quote. 

    It says in Fataawa al-Lajnah al-Daa’imah, 23/124: 

    If you swear by Allah not to take something in the future, 
    then this is regarded as an oath that one must adhere to if adhering to it 
    is an act of obedience to Allah. But if adhering to it is an act of 
    disobedience to Allah and His Messenger, or you think that something else is 
    better than it, then you may break your oath by doing something that is 
    contrary to what you swore to do. End quote. 

    Fataawa al-Lajnah al-Daa’imah, 
    13/124 

    See also the answer to question number
    9985.