How does marriage continue after death, and if it does, how can a man marry his deceased wife's sister, and why does a widow remarry after her husband, and what is the authenticity of the hadiths that indicate a wife remaining with her husband in the Afterlife?

The jurists state that the marriage bond (Nikah (definition)) is severed by death, and this is supported by the permissibility of marrying the sister of the deceased wife. The Hanafis differentiate between the death of the wife, where the marriage bond is severed upon her death and he is not permitted to wash her, and the death of the husband, where the marriage bond is not severed until after the 'iddah (definition) (waiting period) and she is permitted to wash him. As for the Malikis, they hold that the "ruling of marriage" ends with death, while the Shafi'is believe that the "effects of marriage" are not lifted by death.

Among the effects of marriage that remain after death are: one spouse washing the other. The jurists have unanimously agreed on the permissibility of a wife washing her husband, and the majority agree on the permissibility of a husband washing his wife. Also among these effects is the wife being with her husband in Paradise, based on the Almighty's saying: ﴿Enter Paradise, you and your spouses, in happiness.﴾ (Az-Zukhruf/70), and the wife in Paradise belonging to her last husband in this world.

Although the basic principle is that the rulings of marriage cease upon the death of one spouse, some effects remain in this world and the hereafter. As for the wives of the Prophet (peace be upon him), their marriage bond is not severed by death, and its rulings, such as the prohibition of marrying them and the obligation of their maintenance and dwelling, remain, because death, in his case (peace be upon him), is akin to an absence.