He swore by something other than Allaah that he would divorce his wife
Question

                What is the ruling on one who swears by something other than Allaah that he would divorce his wife?.
Praise be to Allah.
    Swearing by anything other than Allaah, such as the Ka’bah or 
    the Prophet (blessings and peace of Allaah be upon him) or any righteous 
    person or by the head of so and so or by the honour of so and so -- all of 
    that is shirk, as it says in the saheeh hadeeth: “Whoever swears by anything 
    other than Allaah has committed shirk.” and the Prophet (blessings and peace 
    of Allaah be upon him) said: “Do not swear by your fathers or by the rivals 
    (of Allaah), and do not swear by Allaah unless you are speaking the truth.” 

    If a person swears by anything other than Allaah, he is not 
    obliged to fulfil his oath, because it is an oath that is not to be 
    honoured. The words of the questioner are general and open to different 
    interpretations. If you meant what I have mentioned above, then he is not 
    obliged to do anything, whether it is offering expiation or anything else, 
    and he is not obliged to go ahead with the divorce. But if what the 
    questioner meant was swearing to divorce, such as saying: If you speak to so 
    and so, then you are divorced, or If I do such and such, then my wife is 
    divorced -- this is a matter concerning which the scholars differed. Some of 
    them say that divorce takes place for the one who breaks this oath. Some of 
    them say that if the intention of the one who swears the oath is to prevent 
    himself or someone else from doing a certain action, or encouraging a 
    certain action, then his divorce does not take place and he has to offer 
    expiation. This is the view which was approved of and favoured by Shaykh 
    al-Islam Ibn Taymiyah (may Allaah have mercy on him), and it has been expressed in fatwas by many of the modern scholars, including our Shaykh, ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him). And Allaah knows best. May Allaah send blessings and peace upon our Prophet Muhammad.