Fath al-Rabbani

Benefits: … A marriage (nikah) can take place without specifying a dower (mahr), but the negation of mahr itself should not occur. If mahr is negated, then the marriage will be invalid. If mahr is not negated but has not been specified, then whatever is mutually agreed upon later will be considered the mahr. And if there is no agreement, then the mahr will be determined by considering the woman's personal and familial status, for example: the general mahr of her sisters, paternal aunts, or other similar women. This is called mahr mithl (equivalent dower). In the narration of Sunan Abu Dawood, it is also clarified that when people testified in favor of the decision of Sayyiduna Abdullah ibn Mas'ud radi Allahu anhu, saying that the Messenger of Allah sallallahu alayhi wa sallam had made the same decision regarding Sayyidah Barwa’ radi Allahu anha and her husband Sayyiduna Hilal ibn Murrah Ashja‘i radi Allahu anhu, then Sayyiduna Ibn Mas'ud radi Allahu anhu became very pleased upon hearing this, that his ijtihadi (independent juristic) decision coincided with the decision of the Messenger of Allah sallallahu alayhi wa sallam.