Is stipulating the divorce of another existing wife as the dower (mahr) valid?

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The specification (tasmiah) of the divorce of another wife as the dower for a new marriage is invalid. The wife is entitled to the customary dower (mahr al-mithl). This is the preferred position of Abu Bakr and the majority of jurists. The basis for this is that such a stipulation does not constitute property, contradicting the divine command concerning marriage (Quran 4:24), which permits seeking wives with wealth. Furthermore, the Prophet - peace be upon him - forbade a woman asking for the divorce of her co-wife to take her place, stating she is only entitled to what is ordained for her. Another narration states it is impermissible for a man to marry a woman in exchange for the divorce of another. This is analogous to using prohibited benefits, such as wine, as dower.