A marriage solemnised between a Hindu girl and a Muslim boy is completely valid if it is registered under the Special Marriage Act. If it is done under any of the personal laws then the marriage will not valid. Either or the party will have to convert into the religion of the other and then get married to register it under any of the personal laws.
Islam strongly advocates for marriage and does not promote celibacy. Marriage under the Islamic law is a contract and not a sacrament like in Hindu law. Under the Muslim law, marriage between a Muslim and a Hindu is not considered as a valid marriage. And therefore, several rights do not arise in such a marriage. However, according to Supreme Court, children born out of such marriage are legitimate and are entitled to claim a share in fatherÕs property.
This is the category in which the marriage between a Muslim and a Hindu falls until the Hindu partner converts to either Islam or Christianity or Judaism in case of wife or to only Islam in case of husband. A fasid marriage is an irregular marriage under the Muslim law which is rendered irregular due to lack of some formality or due to some impediment which can be rectified. Though the irregularities do not make the marriage unlawful, the irregularity must be done away with for the marriage to become valid.
Among the several reasons that make marriage under Muslim law irregular or fasid, one is the difference of religion. The difference of religion does not render a marriage irregular if the wife, if she is not a Muslim, converts to Islam, Christianity or Judaism and in the case where the husband is not a Muslim, if he converts to Islam.
Reference: The Special Marriage Act, 1954