It has two cases:
The first case is: A husband would be essential in the contract and a guardian of the bride in the same time, such as a cousin when he becomes the girl's guardian and in the same time wants to marry her; is it permissible that he would undertake both sides of the contract?
Scholars have differed according to two views:
The first view is: The view of the Hanafi school of fiqh, not including Zufar, the Maiki school of fiqh in its famous view, and the Hanbali school of fiqh in one narration who hold the view that a woman's guardian, who may marry her by her permission, may undertake both sides of the contract by himself and held the following as a proof:
Allah (may He be Exalted) says: "They ask your legal instruction concerning women, say: "Allâh instructs you about them, and about what is recited to you in the Book concerning the orphan girls whom you give not the prescribed portions (as regards Mahr and inheritance) and yet whom you desire to marry." (1)
It was reported from `A'ishah (may Allah be pleased with her) said: "The previous Ayahs has been revealed regarding the case of a man who has an orphan girl, and he is her guardian and her heir. The girl shares with him all his property, even a date-palm (garden), but he dislikes to marry her and dislikes to give her in marriage to somebody else who would share with him the property she is sharing with him, and for this reason that guardian prevents that orphan girl from marrying. So, this Verse was revealed." (2)
The argumentation of this Ayah is Allah's Saying: "whom you give not the prescribed portions (as regards Mahr and inheritance) and yet whom you desire to marry." indicated admonishment, which indicates that a guardian gives the woman in his custody in marriage by his decision alone and if he does not do it by his decision alone, admonishment will have no meaning here because it will not be effective.
Allah's Saying: "And marry those among you who are single (i.e. a man who has no wife and the woman who has no husband)." (3)
This is a command with marriage without distinction between marrying girls by himself or by giving them in marriage to others. And because of what has been reported that `Abdur-Rahman ibn `Awf said to Um Hakim bint Qarizh: "Would you give me the power to conclude your marriage? She said: Yes. He said: I take you in marriage." (4) This is how did they conclude their marriage.
A guardian in this case owns offer and acceptance, so it is permissible for him to undertake both as if he gives his slave girl in marriage to his young slave.
Moreover, it is a contract that was concluded by the offer of a guardian who has full authority and acceptance from a husband who is qualified for marriage, so it will be valid as if it is concluded by two separate persons. (5)
The second view is: The view of Zufar from the Hanafi school of fiqh, the Shafi`y school of fiqh, and one narration of the Hanbaly school of fiqh that it is not permissible for a guardian who wants to marry the woman who is under his custody to undertake both sides of the contract, but he should authorize someone else to give her in marriage to him by her permission because of the Hadith of Al Mughirah ibn Shu`bah when he betrothed the woman under his custody, he commanded a person to give her in marriage to him.
6- It is a contract which a person concludes by permission, so it is not permissible for him to undertake both sides of the contract exactly as the sale contract. (7)
The preponderant saying is the first because the Companions (may Allah be pleased with them) did that without disagreement. Furthermore, there is no contradiction between the action of Al Mughirah and the action of `Abdul-Rahman because both matters are permissible. This woman has a guardian who does not prevent her of marriage, so why does another person undertake her guardianship? Allah knows the best.
1- Surat An-Nisa': 127.
2- The interpretation of the Glorious Qur'an 2/424.
3- Surat An-Nur: 32.
4- Reported by Al Bukhari [without mentioning the full chain of transmission] (Fathul-Bary 9/188- As-Salafiyyah Edition) however Ibn Sa`d mentioned the full chain of narration in At-Tabaqat as in At-Taghliq of Ibn Hajar (4/416- Al Maktab Al Islamy Edition).
5- Al Bahr Ar-Ra'iq 3/146, Bada'i` As-Sana'i`2/231, Mughny Al Muhtaj 3\163, and Al Mughny 7\360, Kash-shaf Al Qina` 5\62,` Al Mubdi` Sharh Al Muqni` 7/39, and the Kuwaiti Islamic Jurisprudence Encyclopedia 41/244.
6- Reported by Al Bukhari [without mentioning the full chain of transmission] (Fathul-Bary 9/188- As-Salafiyyah print) however Al Bayhaqy mentioned the full chain of narration in Al Khilafiyyat as in At-Taghliq of Ibn Hajar (4/416).
7- Bada'i` As-Sana'i` 2/231, Tabyin Al Haqa'iq 2/132, Al Khitab 3\439, Mughny Al Muhtaj 3\163, Al Mughny 7\360, Al Mubdi` Sharh Al Muqni` 7/39.