Imam al-Shafi'i (may Allah have mercy on him) says: It has been narrated from the Prophet (peace and blessings be upon him), may my father and mother be ransomed for him, that he gave judgement concerning Birwa' bint Washiq (may Allah be pleased with her), who had been married without a dowry and then her husband died: "The Messenger of Allah (peace and blessings be upon him) awarded her the dowry of her peers (mahr al-mithl) and awarded her inheritance." If this is established from the Prophet (peace and blessings be upon him), then it takes precedence over everything for us; there is no proof in the saying of anyone other than the Prophet (peace and blessings be upon him), however many they may be, nor in analogy; before his saying there is nothing but obedience to Allah by submitting to it. But if it is not established from the Prophet (peace and blessings be upon him), then no one may attribute to him what is not established; and I have not yet come to know it through a route whose like is established: once it is narrated from Ma'qil bin Yasar (may Allah be pleased with him), once from Ma'qil bin Sinan (may Allah be pleased with him), and once from some man of Ashja' who is not named.
So if the husband or the wife dies, she has neither a dowry nor provision (mut'ah).
The Shaykh (may Allah have mercy on him) said concerning the hadith of Birwa' bint Washiq: This is the disagreement that al-Shafi'i mentioned; however, Abd al-Rahman bin Mahdi is one of the imams of hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14410