One of the pillars of ( temporary )marriage in islam.
Mahr
Useful information: The contract must mention a dower of known property, whether in cash or kind, whose amount is safe from increase or decrease. In order to gain knowledge of the property, it is sufficient for the woman to see it, but it is not necessary that it actually be weighed, measured, or counted-whatever the case may require. The contract of mut'a is not simply an exchange of goods, but a marriage. Even if it is defined as a 'rental', that also is different from an exchange. Hence it is sufficient that any possibility of misunderstanding which might arise from not seeing the dower be removed. As for goods which are not present, it is sufficient that the dower be described in such a manner that the woman's ignorance will be removed, i.e., that it be described exactly as it is.
There is no condition or requirement concerning the amount of the dower except that the two sides come to an agreement over articles which may properly be exchanged, even if they are no more than a few grains of wheat. On this point there are specified hadith as well as the general hadith which state that a woman who enters into mut'a is 'rented'. If the dower is not mentioned, the contract is unanimously held to be invalid, On this point also there are a number of hadith.
The woman may ask for the whole amount of the dower at the beginning of the marriage. In this case, the man may not take back any of the dower under any circumstances, unless for some reason the contract should have been invalid from the beginning (see below). Several hadith are recorded which establish this point without question.