Is a husband's waiver of his right to take back his wife after a revocable divorce valid, given that the waiver was made under duress?

The majority of scholars hold that a separation resulting from khul' (divorce at the wife's instance with compensation) or divorce for a financial consideration renders the woman irrevocably separated, and the husband cannot take her back without a new marriage contract. As for a divorce without compensation, the husband retains the right to take her back during her 'iddah (waiting period). The agreement of both spouses to waive the right of return in a revocable divorce is a matter of scholarly disagreement. The correct view is that the right of return is a right belonging to Allah Almighty, and they are not permitted to agree to waive it. Issues involving disputes and litigations cannot be resolved by a fatwa (religious edict); rather, they must be referred to the Sharia court.