As for the reasoning, it is that this woman has waived her right before it became established, since maintenance becomes due after the marriage contract, whereas she waived it before it became due; therefore, this is not valid.
Thus, if he stipulates that he will owe no maintenance and the marriage contract is concluded, then she subsequently demands maintenance from him and he says, “I stipulated that I would owe no maintenance,” he is nonetheless required to provide maintenance.
But if, after the marriage contract, the wife sees that her husband is going to divorce her and fears that he will do so, and she says to him, “Keep me as your wife without maintenance,” and he agrees, this is permissible, because it is a waiver of a right after it has become established. However, the scholars said: if she later returns and demands it, she is entitled to maintenance, because she has the right to claim it for the future. Maintenance is renewed day by day. This is correct, unless this occurs by way of reconciliation: for example, where discord between the spouses is feared and they reconcile on the basis that there will be no maintenance. In that case, he is not required to provide maintenance, because that is the purpose of reconciliation. If we were to say that, after reconciling on the basis of no maintenance, she may later demand maintenance, then the reconciliation would be meaningless and of no benefit.
In summary:
First: If the husband stipulates, before the marriage contract, that there will be no maintenance, and then concludes the contract on this condition, the contract is valid but the condition is invalid.
Second: If the woman waives her maintenance after the marriage contract, the waiver is valid; however, she may demand it in the future.
Third: If this takes place between them as a reconciliation, where discord between them is feared and they reconcile on the basis that there will be no maintenance, then she may not demand maintenance, because the reconciliation was concluded on that basis; for the purpose of reconciliation is that it be upheld