What makes a shighar marriage invalid: is it the condition that each man marry his ward to the other, or not naming a dowry for each woman?

"Shighar" is a reciprocal marriage in which a man marries his ward (a woman under his guardianship) to another man, on condition that the other man marries his ward to him, with the private parts of each woman serving as the mahr (dowry) for the other. Scholars have differed in its definition. The Hanbalis believe that it also includes silence about the mahr or a condition to negate it.

Scholars have reached a consensus on its impermissibility, but they differed on its validity. The majority considers it void, while the Hanafis hold it to be valid, with the mahr being obligatory. The reason for its invalidity stems from the absence of a real mahr for the private parts of each spouse, and from making the private parts of one woman the mahr for the other, in addition to the contingency and suspension between the two contracts.