Ja'far bin Muhammad narrates from his father that Sayyidah Umm Kulthum bint Ali (may Allah be pleased with them both) and her son Zayd bin Umar bin al-Khattab died on the same day, and it could not be known which of them died first; so she did not inherit from him, nor did he inherit from her. Likewise, the martyrs of the Battle of Siffin and of the Event of al-Harrah did not inherit from one another. The chain of this hadith is sahih (authentic). It contains points of benefit, one of which is that Sayyidah Umm Kulthum (may Allah be pleased with her) bore Sayyiduna Umar (may Allah be pleased with him) a son; and for the other point of benefit there is a supporting narration:

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that he would not make one deceased person the heir of another deceased person when it was not known which of them died before the other.

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) concerning the saying of Allah Almighty: "And those with whom you have made pledges, give them their share" [Surah al-Nisa: 33] , that he said: (Previously) a man would make a pact with another man, even though there was no blood relationship between them, so that each could inherit from the other; then Allah Almighty abrogated this through this verse of Surah al-Anfal: "And blood relatives are more entitled to one another in the Book of Allah" [Surah al-Anfal: 75] .

It is narrated from Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) that he said on the pulpit (while delivering a sermon) that he had distributed the inheritance of a man who left a daughter and a sister, and he fixed half for the daughter and (the remaining) half for the sister, while the Messenger of Allah (peace and blessings be upon him) was alive among them at that time. This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.