What is the meaning of the hadeeth “Leave that which makes you doubt for that which does not make you doubt”?
Question

                I would like an explanation of the hadeeth: “Leave that which makes you doubt for that which does not make you doubt”.
Praise be to Allah.
    This hadeeth was narrated by at-Tirmidhi 
    (2442), Ahmad (1630) and Ibn Hibbaan (722) from al-Hasan ibn ‘Ali (may Allah 
    be pleased with him) who said: I memorized from the Messenger of Allah 
    (blessings and peace of Allah be upon him): “Leave that which makes you 
    doubt for that which does not make you doubt, for truth leads to reassurance 
    and lies lead to uncertainty.” Classed as saheeh by Shaykh al-Albaani (may 
    Allah have mercy on him). 

    It was also narrated by an-Nasaa’i 
    (5614) without the additional words “for truth leads to reassurance…” 

    Al-Mannaawi (may Allah have 
    mercy on him) said: “Leave that which makes you doubt” means: refrain from 
    that which you are uncertain as to whether it is good or bad, halaal or 
    haraam

    “for that which does not make 
    you doubt” that is: turn instead to that about which you are not uncertain, 
    that which you are sure is good and halaal.

    “for truth leads to reassurance” 
    means: the heart is at ease with it

    “and lies lead to uncertainty” 
    means: they make the heart anxious and uneasy. At-Teebi said: This phrase 
    explains the preceding words. What it means is: if you find yourself 
    doubting (and uncertain about) something, then leave it, for the heart of 
    the believer is at ease with the truth and is doubtful about lies and 
    falsehood. Being doubtful about something is an indication that it may be 
    false and wrong, so beware of it; and your feeling at ease with something is 
    an indication that it is true, so take hold of it.

    End quote from Fayd al-Qadeer 
    3/529 

    Shaykh Ibn ‘Uthaymeen (may Allah 
    have mercy on him) said: This hadeeth is an example of concise speech, and 
    how excellent and beneficial it is to follow it. One may feel doubtful about 
    many things, so we say: leave that which you have doubts about for that 
    which you have no doubts about, so that you may be safe and sound. If anything 
    makes you feel doubtful and anxious, then leave it for something that does 
    not make you feel doubtful, so long as this does not reach the level of 
    waswaas (when you start doubting everything). If it does reach the level of 
    waswaas, then do not pay any attention to it. 

    This has to do with acts of 
    worship, interactions with others, marriage and all categories of 
    knowledge. 

    An example of that in the case 
    of acts of worship is that of a man who breaks his wudoo’, then prays, and 
    he is not sure whether he did wudoo’ after breaking it or not. He is unsure, 
    because if he did do wudoo’ then his prayer is valid, but if he did not then 
    his prayer is invalid, so he remains anxious. In this case we say: Leave 
    that which makes you doubt for that which does not make you doubt. The doubt 
    in this case has to do with whether the prayer was valid and not doubting 
    means that you should do wudoo’ and pray. 

    The opposite of the previous 
    example is that of a man who does wudoo’ then prays, and he is not sure 
    whether he broke his wudoo’ or not. 

    In this case we say: Leave that 
    which makes you doubt for that which does not make you doubt. You have 
    something which is certain, which is that you did wudoo’, then you were not 
    sure whether this wudoo’ was broken or not. What you should ignore is the 
    doubt or uncertainty as to whether the wudoo’ was broken or not. So calm 
    down and ignore that doubt or uncertainty.

    End quote from Sharh al-Arba‘een 
    an-Nawawiyyah, p. 155 

    This hadeeth is a basic 
    principle in the area of being prudent and is encouragement to ignore 
    doubts. It is also a basic principle in the area of following that which is 
    certain and ignoring that which is dubious. 

    Al-Haafiz Ibn Rajab (may Allah 
    have mercy on him) said:

    This hadeeth highlights the 
    importance of being careful when faced with doubtful and dubious matters, 
    and keeping away from them, because in the case of that which is definitely 
    halaal, the believer will have no doubt in his heart concerning it – and 
    doubt here means anxiety and worry – rather he will feel at ease and will 
    have reassurance in his heart. As for that which is doubtful, he will feel 
    anxiety and worry concerning it.

    End quote from Jaami‘ al-‘Uloom 
    wa’l-Hukam, 1/280 

    And Allah knows best.