Praise be to Allah.
There is nothing wrong with buying a dress for the woman to wear for her wedding, even if it is expensive, so long as it does not reach the level of being extravagant. This varies from one environment and one person to another, but if this dress is only going to be worn once or a few times, as is the case with many women, then it is better not to buy it and to do without it by renting or borrowing a dress, and saving the money that would be paid for it. That is better and more useful.
If the woman wants to buy this dress, then she should choose something that she can wear for her wedding and on other occasions, so as to save money, hers and her husband’s. The Prophet (blessings and peace of Allah be upon him) forbade wasting money, and Allah, may He be exalted, condemns spendthrifts and states that they are the brothers of the devils.
There are some righteous women who are very well off; one of them may buy a dress for her own wedding, then make it a waqf for the benefit of her sisters, so that they can wear it for their weddings. This is a good idea.
For more information, please see the answer to question number 12853 .
And Allah knows best.
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