Effect of apostasy on marriage before and after consummation
Question

                If a person apostatises from Islam -- Allah forbid -- and then comes back to Islam before the end of the ‘iddah period and without anyone knowing about this matter, does his wife become permissible for him without renewing the marriage contract? Does this count as one divorce (talaaq)? If he had not consummated the marriage with his wife and he apostatised -- Allah forbid - - does his wife become irrevocably divorced from him straight away regardless of whether he comes back to Islam?.
Praise be to Allah.
      Firstly: 

    If the husband does or says something that implies apostasy 
    from Islam, such as reviling Allah (may He be exalted) or reviling His 
    Messenger (blessings and peace of Allah be upon him) or denying something 
    that is well known to be a basic matter of Islam -- if that happens before 
    consummating the marriage, then the marriage is annulled straight away. 

    Ibn Qudaamah (may Allah have mercy on him) said: If one of 
    the spouses apostatises before consummation of the marriage, the marriage is 
    annulled according to most scholars. But it was narrated from Dawood that 
    (marriage) is not annulled by apostasy, because the basic principle is that 
    the marriage remains as it is. But Allah says (interpretation of the 
    meaning): “Likewise hold not the disbelieving women as wives” 
    [al-Mumtahanah 60:10] and “send them [believing women] not back to 
    the disbelievers. They are not lawful (wives) for the disbelievers nor are 
    the disbelievers lawful (husbands) for them” [al-Mumtahanah 60:10]. The 
    difference in religion means that intimacy is not permissible, which 
    inevitably means annulling the marriage, as is also the case if a woman 
    becomes Muslim whilst married to a kaafir. 

    End quote from al-Mughni, 7/133 

    It apostasy occurs after consummation, should they be 
    separated immediately or should separation be delayed until the end of the 
    ‘iddah? 

    There is a difference of opinion among the fuqaha’ concerning 
    this. 

    The view of the Shafaa‘is, and the correct view according to 
    the Hanbalis, is that if he comes back to Islam before his wife’s ‘iddah 
    ends, then the marriage remains as is. If the ‘iddah ends before he comes 
    back to Islam, then separation takes place and he cannot go back to his wife 
    except with a new marriage contract. 

    The view of the Hanafis and Maalikis is that apostasy means 
    that they must be separated immediately, even if that is after consummation 
    of the marriage. See: al-Mughni, 7/133; al-Mawsoo‘ah al-Fiqhiyyah, 
    22/198; al-Insaaf, 8/216; Kashshaaf al-Qinaa‘, 5/121; 
    Tuhfat al-Muhtaaj, 7/328; al-Fataawa al-Hindiyyah, 1/339; 
    Haashiyat al-Dasooqi, 2/270. 

    Some of the scholars say that if he repents after the ‘iddah 
    ends, he may go back to his wife if she agrees to that and she has not 
    married someone else. 

    See: Fataawa Arkaan al-Islam by Shaykh Ibn ‘Uthaymeen, 
    p. 279, as well as the answer to question no.
    21690. 

    Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: To 
    sum up, one of three scenarios must apply in the case of the husband who 
    gives up prayer: 

    (i)If that happens before the 
    marriage contract is done, the marriage is not valid and the wife does not 
    become permissible thereby.

    (ii)If that happens after the 
    marriage contract is done and before the marriage is consummated or the 
    couple spends time alone together, which would make the ‘iddah obligatory, 
    the marriage is annulled as soon as he gives up prayer.

    (iii)If that happens after the 
    marriage was consummated or the couple spent time alone together, which 
    would make the ‘iddah obligatory, it depends on whether the ‘iddah has ended 
    or not. If he repents and begins to pray before the end of the ‘iddah, then 
    she is still his wife, but if he does not do that, then when the ‘iddah 
    ends, the marriage is annulled from the time he apostatised -- Allah forbid. 
    In that case, if he comes back to Islam, (according to some scholars) he may 
    take her back if he wants or (according to other scholars) he may not. There 
    is a difference of opinion among the scholars concerning this issue. End 
    quote from Fataawa Noor ‘ala al-Darb.

    Secondly: 

    The annulment that takes place because of apostasy is not 
    regarded as being talaaq (divorce) according to the majority of fuqaha’. 

    It says in al-Mawsoo‘ah al-Fiqhiyyah (7/34): If one of 
    them apostatises before the marriage is consummated, then the marriage is 
    annulled immediately and neither of them can inherit from the other. 

    If that occurred after the marriage has been consummated, the 
    Shaafa‘is say -- and this is also narrated in one report by the Hanbalis -- 
    they should be separated until the end of the ‘iddah. If he comes back to 
    Islam before the ‘iddah ends, then the marriage remains valid, but if he 
    does not come back to Islam, the marriage is annulled with no divorce (talaaq) 

    Abu Haneefah and Abu Yoosuf said -- and it is also narrated 
    in one report by the Hanbalis -- that the apostasy of one of the spouses 
    annuls the marriage immediately, and that does not count as a talaaq 
    divorce, whether it occurs before consummation or afterwards. 

    The Maalikis said, and this is also the view of Muhammad ibn 
    al-Hanafiyyah: If one of the spouses apostatises, the marriage is annulled 
    with an irrevocable divorce (talaaq). End quote. 

    And Allah knows best.