If a person wants to cancel his intention whilst doing wudoo’, praying or fasting
Question

                The great scholar al-Sa’di says in al-Fataawa al-Sa’diyyah (p. 228): Cancelling one’s intention with regard to acts of worship is of two types: one which does not have any effect, which is after the act of worship has been completed. … The second is cancelling the intention for the acts of worship when one is still doing it. … This means that the act of worship is not valid. 

Does this mean that if it occurs to me to break an obligatory fast, my fast becomes invalid? What if that occurs to me but I do not form the intention to break my fast, is that o.k.? What is the ruling on that?  Similarly in the case of wudoo’, if in the middle of it I begin to doubt whether there is some urine there, for example, then I do not find any. Sometimes I form the intention to stop doing wudoo’, then I go back and complete it after not finding anything. Should I start again from scratch because I stopped intending wudoo’ in this case?.
Praise be to Allah.
    If a person forms the intention to stop doing an act of 
    worship whilst he is doing it, it becomes invalid. No exception is made 
    except in the case of Hajj and ‘umrah, which do not become invalid if the 
    intention is cancelled or even if a person declares that he is going to 
    stop. Rather the muhrim remains in ihraam until he has completed the rituals 
    or he exits ihraam because of being prevented from continuing.  

    It says in al-Mughni (1/278): If he started his prayer 
    with a sound intention, then he forms the intention to stop praying and exit 
    from it, then it becomes invalid. This was the view of al-Shaafa’i. End 
    quote. 

    It says in Zaad al-Mustanqi’ in the chapter on prayer: 
    If he decides to end his prayer whilst praying or he becomes hesitant, then 
    his prayer is invalidated. In the chapter on fasting he said: The one who 
    forms the intention to break the fast has broken the fast. 

    But Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said 
    in al-Sharh that hesitating about ending the prayer does not make the 
    prayer invalid. See: al-Sharh al-Mumti’ (1/486). An example of 
    hesitating is if he hears someone knocking at the door, and he wonders 
    whether he should stop praying or carry on? 

    Thus it is clear that if a person decides to stop the act of 
    worship, it becomes invalid, but if that was simply a thought that crossed 
    his mind, it does not invalidate the act of worship. 

    Based on this, if the idea of stopping the fast simply occurs 
    to one, it does not invalidate the fast until he decides and forms the 
    intention to break the fast.  

    Similarly, if whilst doing wudoo’ he becomes uncertain as to 
    whether urine has come out of him, and he pauses and looks, but does not 
    intend to stop doing wudoo’, and he does not find anything, then his wudoo’ 
    is not invalidated. 

    Similarly if he intends to stop doing wudoo’ his wudoo’ is 
    invalidated, and it is not permissible for him to complete it, rather he 
    must start all over again. 

    It says in al-Insaaf (1/151): If he cancels his 
    intention whilst purifying himself, what he has already done is invalidated, 
    according to the correct view. This was the view favoured by Ibn ‘Aqeel and 
    by al-Majd in his commentary. And it was said that what has already been 
    done is not invalidated thereby; this was stated by al-Musannaf in 
    al-Mughni. End quote. 

    But one must beware of waswasah, because the shaytaan may 
    come to a person and make him think that something has come out of him, and 
    the person may get carried away with that and hardly be able to do any act 
    of worship without doubting about it, which may cause him hardship and 
    distress. Please see question no. 
    62839. 

    And Allaah knows best.