Assalamualaikum, what is the ruling for a husband that use or eat from the mahar that was given to his wife?
Waalaikumussalam Warahmatullah Wabarakatuh.
Alhamdulillah, praise and thanks to Allah for the many countless blessings He has blessed us all with. Blessings and salutations to the Prophet Muhammad PBUH, his family, companions and all those that follow his teachings to the day of judgement.
Islam is a religion that honours the marriage institution, and place women at a high standing. One of the proofs of this statement is the sanctioning of mahar in marriage.
The Concept of Mahar in Islam
Literally, mahar means:
ما يَدْفَعُهُ الزَّوْجُ إِلَى زَوْجَتِهِ بِعَقْدِ الزَّوَاجِ
“What is paid by a husband to his wife as a gift for aqad (marriage).”
According to syarak, as defined in mazhab Syafi’e:
هُوَ مَا وَجَبَ بِنِكَاحٍ أَوْ وَطْءٍ أَوْ تَفْوِيتِ بُضْعٍ قَهْرًا 
“Mahar is something that is obligated due to marriage, intercourse or rape.”
The sanctioning of mahar is commanded through the verse of the Quran:
وَآتُوا النِّسَاءَ صَدُقَاتِهِنَّ نِحْلَةً فَإِنْ طِبْنَ لَكُمْ عَنْ شَيْءٍ مِنْهُ نَفْسًا فَكُلُوهُ هَنِيئًا مَرِيئًا
“And give the women [upon marriage] their [bridal] gifts graciously. But if they give up willingly to you anything of it, then take it in satisfaction and ease.”
Surah al-Nisa’ (4)
Hence, mahar in the form of payment or gift is an obligation for a husband towards his wife. Allah SWT reproach husbands that take back the mahar they have given to their wives. It is stated in the Quran:
وَإِنْ أَرَدْتُمُ اسْتِبْدَالَ زَوْجٍ مَكَانَ زَوْجٍ وَآتَيْتُمْ إِحْدَاهُنَّ قِنْطَارًا فَلَا تَأْخُذُوا مِنْهُ شَيْئًا أَتَأْخُذُونَهُ بُهْتَانًا وَإِثْمًا مُبِينًا 20 وَكَيْفَ تَأْخُذُونَهُ وَقَدْ أَفْضَى بَعْضُكُمْ إِلَى بَعْضٍ وَأَخَذْنَ مِنْكُمْ مِيثَاقًا غَلِيظًا
“But if you want to replace one wife with another and you have given one of them a great amount [in gifts], do not take [back] from it anything. Would you take it in injustice and manifest sin? And how could you take it while you have gone in unto each other and they have taken from you a solemn covenant?”
Surah al-Nisa’ (20-21)
In marriage, the wife has absolute ownership of her mahar, it is not partially owned with her wali or family members.
The Ruling for a Husband Using His Wife’s Mahar
A question the arises; is it permissible for a husband to use the mahar he has given to his wife?
Al-Imam Ibnu Kathir comments on verse 4, Surah al-Nisa’: “It is the obligation of a husband to give the mahar of his wife graciously; if his wife willingly gives some or all of her mahar back to her husband, then the husband should accept it as something that is good and permissible.” 
In Tafsir al-Munir written by Almarhum Dr Wahbah al-Zuhaily:
“It is permissible for a wife to give her mahar that she gets from her marriage to her husband, or some of her mahar.” 
Then he further adds:
“The generality of the Quranic verse shows the permissibility, whether the wife is a virgin or a widow when she is married to her husband; this is the opinion of the majority of the scholars.” 
Whereas, in al-Mausu'ah al-Fiqhiyyah:
“The majority of the fuqaha hold the opinion that a husband cannot benefit from (using) anything that belongs to his wife, whether a bed, containers and others without the consent of his wife, whether the property is a gift from him or a gift from someone else, or whether the wife received her mahar or not. The wife has absolute right to use her possessions as she likes, to donate, give or exchange, as long as it does not bring harm to her.” 
- It is prohibited for a husband to eat/use/benefit from his wife’s mahar without the consent and permission of his wife, for the wife is the absolute owner of her mahar and this has been declared by Allah SWT in the Quran.
- It is permissible for a husband to eat/use/benefit from the mahar of his wife, if his wife willingly consents to it.
 Al-Mausu’ah al-Fiqhiyyah al-Kuwaitiyyah 39/151
 Mughni al-Muhtaj 3/220
 Ibn Kathir. Tafsir al-Qur’an al-‘Azim, 2/213
 Tafsir al-Muneer, 4/241
 Al-Mausu'ah Al-Fiqhiyah Al-Kuwaitiyyah, 26/286