Praise be to Allah.
The majority of scholars are of the view that the mahr stipulated should be wealth, or some benefit for which it is valid to receive payment – such as teaching the wife sound knowledge. This is indicated by the verse in which Allah, may He be exalted, says (interpretation of the meaning):
“And lawful to you are [all others] beyond these, [provided] that you seek them [in marriage] with [gifts from] your property, desiring chastity, not unlawful sexual intercourse”
It says in al-Mawsoo‘ah al-Fiqhiyyah (39/155, 156):
The majority of fuqaha’ – Maalikis, Shaafa‘is and Hanbalis – are of the view that with regard to anything that may be used to make a purchase, any item that has a value and any benefit for which one may charge payment, it is permissible to make it a mahr. …
The Hanafis stated clearly that the mahr must be a type of wealth to which people give a value. So if they agree on a type [and quantity] of wealth as a mahr, then that is valid, otherwise it is not valid.
The majority are of the view that it is permissible for the mahr to be benefits for which it is possible to receive payment.
It also says in al-Mawsoo‘ah (39/156):
The Maalikis, according to the well-known view, and the Shaafa‘is and Hanbalis, are of the view that it is permissible for a benefit to be a mahr, in accordance with their principle that with regard to anything for which it is permissible to receive payment, it is valid to call it a mahr. Therefore it is valid to make the use of his house, mount or slave for one year a mahr for his wife, or to make her mahr his serving her in tilling the land, building a house, sewing a garment, or taking her for Hajj, for example. End quote.
Thus it becomes clear that the four imams did not allow the kind of mahr asked about here, and they regarded that as not valid, because if a man memorizes the Qur’an, it is not a benefit with a value that the husband is offering to his wife, so that it could be a mahr for her. Such a thing cannot be regarded as a valid mahr.
That is unlike the case if her mahr is that he will teach her some parts of the Qur’an; that is valid according to the more correct scholarly opinion, because teaching involves some effort and time, by doing that, he is usually offering something of value to the other person.
With regard to the report that Umm Sulaym (may Allah be pleased with her) stipulated that Abu Talhah should become Muslim, and she took his becoming Muslim as her mahr, that was narrated by an-Nasaa’i (3441) from Anas ibn Maalik (may Allah be pleased with him), who said:
Abu Talhah proposed to Umm Sulaym, and she said: By Allah, O Abu Talhah, a man such as you is not to be rejected, but you are a disbelieving man, and I am a Muslim woman, and it is not permissible for me to marry you. If you become Muslim, that will be my mahr and I will not ask you for anything else. So he became Muslim, and that was her mahr.
Thaabit said: I never heard of any woman whose mahr was nobler than that of Umm Sulaym, for it was Islam.
This report was classed as saheeh by Ibn Hajar in Fath al-Baari (9/115) – and he responded to those who criticized its text. It was also classed as saheeh by al-Albaani in Saheeh an-Nasaa’i.
The apparent meaning of the hadith indicates that it is permissible to make the husband’s becoming Muslim a mahr, and that is definitely not any kind of wealth.
This may be answered in two ways:
Firstly, that was by way of venerating Islam, not by way of making his becoming Muslim a mahr for her, so he must have given her something as a mahr, even if it was little. But because the marriage depended on that, and it would show how serious he was in his wish to marry Umm Sulaym, the mahr was insignificant in comparison to his becoming Muslim. Hence it is not mentioned in the hadith.
At-Tahhaawi said: His becoming Muslim was not actually a mahr; rather what is meant is that he married her as a result of his becoming Muslim. Some narrators added to the hadith of Anas that Anas said: By Allah, she did not have any mahr apart from that. What this means in our view – and Allah knows best – is that she did not want any mahr apart from that.
End quote from Sharh Ma‘aani al-Athaar (3/17).
Ibn ‘Abd al-Barr said: Nothing is said about the mahr, because usually it is a given. …
What this means is: when he became Muslim, it became permissible for him to marry her, and nothing was said about the mahr.
End quote from at-Tamheed (21/119).
Secondly: the marriage of Umm Sulaym took place before the verses enjoining the mahr were revealed, because Abu Talhah was one of the first of the Ansaar to become Muslim, as he was present at the Battle of Badr and was a prominent figure. adh-Dhahabi said of him: He was one of the most prominent of those who were at Badr.
End quote from as-Siyar (3/356).
Ibn Hazm said concerning the story of the marriage of Umm Sulaym (may Allah be pleased with her): It took place sometime before the Messenger of Allah (blessings and peace of Allah be upon him) migrated, because Abu Talhah had been Muslim for a long time and was one of the early Muslims, at a time when the obligation of giving women their mahrs had not yet been revealed.
End quote from al-Muhalla (9/98).
Whatever the case, what you should do, so that the mahr will definitely be valid, is come to an agreement with the husband on a certain amount of wealth, which is to be the mahr, even if it is small. Then after that, there is nothing wrong with stipulating that he should memorize some parts of the Qur’an before the marriage takes place.
For more information, please see the answer to question no. 213663.
And Allah knows best.