Praise be to Allah.
In the answers to questions no. 32716 and 145955 we explained that it is permissible for the entire mahr to be expedited or for the entire amount to be deferred, or some of it may be expedited and some of it may be deferred, and the deferred portion is regarded as a debt that is owed by the husband, which he must pay off when it becomes due, like any other debt. If he has not stipulated any time for it to be paid, then he must pay it off if he divorces her, and it must be paid off from what he leaves behind if he dies.
If the husband becomes able to pay off the deferred portion of the mahr before it becomes due, that is good and is paying off his debt and freeing himself of obligations, and it will protect the wife’s rights from being lost in the event of his death, as usually happens, and will prevent any problems due to this cause in the event of divorce and the like.
The Standing Committee was asked:
When my marriage contract was done, my husband gave me the expedited portion of the mahr, and the remainder was written down in the marriage contract as deferred, to be paid in the event of one of two things: either his death or divorce. My question is: do I have the right to take it before either of these events occurs i.e., whilst my husband is still alive? Because he wants to give me this money by his own choice, without divorce occurring. Do I have the right to take the deferred portion?
The committee replied:
It is permissible for you to take the deferred portion of your mahr before the stated time occurs (before it is due), if your husband gives it to you by his own choice.
End quote from Fataawa al-Lajnah ad-Daa’imah (19/64)
The deferred portion of the mahr may be written in the marriage contract or otherwise, in a manner that will guarantee the agreed-upon rights of the woman.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
The Sahaabah did not write down mahrs because they did not get married with a delayed portion of the mahr; rather they would pay the mahr immediately, and if they delayed it, it would be well-known. But when people began to arrange marriages with a deferred portion to be paid after a long time, and it might be forgotten, they began to write down the deferred portion, and that became proof in confirming the mahr and that she was his wife.
End quote from Majmoo‘ al-Fataawa (32/131)
If the deferred portion of the mahr is given before the time stated in the marriage documents, this does not require changing it in the document, unless that may be done easily. If it is difficult to do it, then a matter such as this has nothing to do with the marriage contract in the first place or the validity of the documents; rather it is just a means of guaranteeing and documenting people’s rights, as explained in the quotation from Shaykh al-Islam Ibn Taymiyah above. But it is sufficient for the spouses to prove, by means of whatever documentation will establish that, that the wife has received the remaining portion due to her of the mahr, lest there arise any dispute when the (originally) stated time for payment of the deferred portion comes.
And Allah knows best.