It is narrated from the sixth Shia Imam, Ja’afar Al-Sadeq (AS) who said: After passing away of the Prophet of Islam (PBUH), his dear daughter Lady Fatimah Al-Zahra (SA) was alive for about 75 days. And the heart-breaking grief of the passing away of the father filled her heart, and for this reason Jibril/Jibrail (AS) used to come to condole and comfort Lady Fatimah Al-Zahra (SA). In these meetings, Jibril (AS) used to talk about her father’s (PBUH) holy status, and sometimes about the events which would happen after the Passing away of the Prophet (PBUH) to his family. Imam Ali (AS) wrote down whatever Jibril (AS) said, and the collection of these sayings by Jibril (AS) is called Mos’haf Al-Fatimah (SA) (the Book of Fatimah (SA)) [1].
[1] Osul Kafi, Vol. 1, Page 349.