There are Shi'a Muslim tradition that can be found in Usul al-Kafi about a book called "Mushaf of Fatimah", which speaks of Fatimah upon the passing of her father, Muhammad. There are several versions of this tradition, but common to all are that the angel Gabriel appeared to her and consoled her by telling her things that she wrote in a book. According to one tradition  they were prophesies. The book, if it was ever physical, did not survive, and was seen to be something that the Mahdi would reveal in the last days .
Sunni do not have any sources regarding such book. Some believe Fatimah's Mushaf means "Fatimah's Qur'an", accusing Shi'as of having their own version of the Qur'an.
Bahá'ís believe that The Hidden Words was revealed by Bahá'u'lláh in fulfillment of this tradition. Indeed, Bahá'u'lláh originally named the book The Book of Fatimah, though he later referred to it in its modern appellation. This aspect of fulfillment corresponds with the Bahá'í beliefs that end times prophecies of all the world's religions are to be interpreted mystically and metaphorically. This puts the Bahá'í understanding of what Gabriel revealed to Fatimah somewhat at odds with the Shi'a traditions.
In practical effect, The Hidden Words bear similarities to the Hadith Qudsi, which are also very spiritual utterances that Muslims hold in high regard. The Hidden Words function in a similar way to the Beatitudes in Christianity or the Psalms in the Hebrew Bible.