Salamu alaykum. In the answer about arwah between spouses What is the 'awrah between husbands and wives? is linked a fatwah of al-Mughni. In the english translate appears that is haram to see the wife vagina for the hadith narrate by Aisha. I thought it was only makrooh because the hadith is daif. Can you clarify this question? Thank you!
First of all al-Mughni is a book on hanbali fiqh not the Qur'an, so whatever the author says is the interpretation of his fiqh school based on their ijtihad and osol and not necessarily the truth as scholars are not infallible.
Nevertheless as you sadly didn't show us the source of the translation I must trust your statement saying:
In the english translate appears that is haram to see the wife vagina for the hadith narrate by Aisha.
Which is clearly in conflict with the Arabic original wording of ibn Qudamah as displayed here:
In the following I will translate from Arabic, this is my own translation take it carefully
وَيُكْرَهُ النَّظَرُ إلَى الْفَرْجِ فَإِنَّ عَائِشَةَ - رَضِيَ اللَّهُ عَنْهَا - قَالَتْ: مَا رَأَيْت فَرْجَ رَسُولِ اللَّهِ - صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ - قَطُّ رَوَاهُ ابْنُ مَاجَهْ
It is frowned upon (makrooh) to look at the private parts based on the hadith of 'Aishah (see also a second version in Sunan ibn Majah).
وَفِي لَفْظٍ قَالَتْ: مَا رَأَيْته مِنْ رَسُولِ اللَّهِ - صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ - وَلَا رَآهُ مِنِّي.
And in a different wording: "I never looked at (or I never saw) it (the private part of) from the Messenger of Allah nor has he seen(looked at) mine"
So ibn Qudamah didn't actually say it is haram , but it is frowned upon (makrooh).