Answered by: Alimah Nasima Umm Hamza
Assalamu Alaikum Wa Rahmatullah
If someone feels a sexual desire like only waswasa or doubt about his daughter does his wife becomes haram for him?
بسم الله الرحمن الرحيم
In the name of Allah, the Most Gracious, the Most Merciful.
It is narrated on the authority of Abu Huraira that the Messenger of Allah (ﷺ) observed:
“Verily Allah forgave my people the evil promptings which arise within their hearts as long as they did not speak about them or did not act upon them.” 
حَدَّثَنَا سَعِيدُ بْنُ مَنْصُورٍ، وَقُتَيْبَةُ بْنُ سَعِيدٍ، وَمُحَمَّدُ بْنُ عُبَيْدٍ الْغُبَرِيُّ، – وَاللَّفْظُ لِسَعِيدٍ – قَالُوا حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ قَتَادَةَ، عَنْ زُرَارَةَ بْنِ أَوْفَى، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم “ إِنَّ اللَّهَ تَجَاوَزَ لأُمَّتِي مَا حَدَّثَتْ بِهِ أَنْفُسَهَا مَا لَمْ يَتَكَلَّمُوا أَوْ يَعْمَلُوا بِهِ “ .
Having these evil thoughts in your head will not annul your marriage.
But it is vital that you realise that thoughts are the beginning of actions, because without a thought entering our minds, inevitably the action would not follow.
It is vital that you remove the thoughts from your head and busy your mind with other thoughts as soon as they enter.
The consequences of such thoughts, when they are brought into action are dire indeed, leaving families torn apart. If the sexual thoughts were to lead you to so much as touch your daughter with desire, then this is enough to break your marriage. 
Take heed, even though the thought itself is not accounted upon, you must not dwell on these thoughts when they enter into your mind, and you must work to remove such ideas from your head permanently before they escalate.
Only Allah Ta’ala knows best.
Written by Alimah Nasima Umm Hamza
Checked and approved by Mufti Mohammed Tosir Miah
 Sahih Muslim, Hadith Number 127a
 Raddul Muhtaar, Volume 3, Pages 35-36
This answer was collected from DarulIftaBirmingham.co.uk, which is run under the supervision of Mufti Mohammed Tosir Miah from the United Kingdom.