Allaah The Exalted forbade the wives of the Prophet sallallaahu `alayhi wa sallam ( may Allaah exalt his mention ) from remarrying after his death as stated in the verse that reads (what means): {And it is not (conceivable nor lawful) for you to harm the Messenger of Allaah or to marry his wives after him, ever. Indeed, that would be in the sight of Allaah an enormity.} [Quran 33:53] The wisdom behind this decree has been highlighted by the scholars. For instance, Al-Qurtubi may Allaah have mercy upon him wrote in his Tafseer,

“Allaah The Exalted forbade marrying the wives of the Prophet sallallaahu `alayhi wa sallam ( may Allaah exalt his mention ) after his death and declared them as Mothers of the believers. This is one of the special privileges granted to the Prophet sallallaahu `alayhi wa sallam ( may Allaah exalt his mention ) to preserve his honor and emphasize his high status to the Muslims … . It was also said that the wives of the Prophet sallallaahu `alayhi wa sallam ( may Allaah exalt his mention ) were not permitted to remarry after him because they will be his wives in Paradise, as the woman will be the wife of her last husband in Paradise. It was narrated that Huthayfah may Allaah be pleased with him said to his wife, "If you want to be my wife in Paradise, don't marry anyone after my death. A woman will be with her last husband in Paradise."”

Since this is Allaah's decree, no one can reject it or be critical of it.

His wives are regarded as mothers of the muslims and it is forbidden to marry one's mother in Islam