Shahr-bánú (literally “The Fairest Lady of the Realm, shahr means dominion/realm and bánú, “fairest, brightest lady”), is said to be the daughter of Yazdgerd III (632-51 CE), the last Zoroastrian Sassanid Emperor. According to the beliefs of the Shiʿites, (also of a substantial number of Sunnis,) she became the wife of the third Imam, Hussain ibn ʿAli, and the mother of the fourth Imam, Zayn ul-ʿĀbedin. Consequently, the lineage of Imams, from the fourth to twelfth and final, would be her progeny.
In his al-Kāmel, the philologist Mobarrad (died 900 CE) seems to have been one of the very first to state that the mother of Imam ʿAli Zayn al-ʿĀbedin, was the daughter of Emperor Yazdgerd. He strongly emphasizes the nobility of the woman and, in general, the grandeur of the Ancient Persians (Mobarrad II, pp. 645-66).
Yaʿqubi (904 CE), Ḥasan b. Musā Nowbaḵti and Saʿd b. ʿAbd-Allāh (both died circa. 912-13 CE) are among the first Shiʿites to allude in passing to the fact that the mother of Imam Zayn al-ʿĀbedin was the daughter of the last Zoroastrian Sassanid Emperor (Yaʿqubi II, pp. 246-47 and 303; Nowbaḵti, p. 53; Ašʿari, p. 70).
Also, Ṣaffār Qomi (died 902-903 CE) delivers a long and detailed version of the account, containing a Hadith or saying attributed to the fifth Imam Moḥammad Bāqer: Accordingly, under the second caliph ‘Omar (reign 634-44 CE), the noble daughter of the last Zoroastrian Sassanid Emperor is brought as a captive to Medina. Light radiating from the fair face of the Zoroastrian princess illuminated the Prophet of Islam’s mosque, where the caliph presides. A prayer in the sacred Avestan language by the Zoroastrian Princess provoked Omar’s wrath.
ʿAli intervened in favor of the young Zoroastrian princess and made it clear to ‘Omar that events unfolding are beyond his understanding and that he should step aside. ʿAli then authorized the Zoroastrian Princess, with whom he spoke in Persian, to freely choose her husband. She chose Ḥussain to whom ʿAli announced the good news that the young woman will be the mother of his child, i.e. the next Imam (Ṣaffār, p. 335, no. 8).
In the Eṯbāt al-waṣiya, attributed to Masʿudi (died 956-57 CE), the story takes place under the caliphate of ‘Omar and in this case two daughters of Emperor Yazdgerd are given in marriage, with ʿAli’s consent to his sons (Masʿudi, p. 170).
In Shaykh Mofid’s (died 1022 CE) account, under ʿAli’s caliphate, the elder daughter of the Persian Emperor, here named shāh-e zanān (lit.: “Ruler of all women” cCompare with the title of Fāṭema, sayyedat al-nesāʾ) marries Ḥussain, while a second unnamed daughter is given in marriage to the son of Abu Bakr, Moḥammad (Mofid, pp. 137-38).
All the Western specialists of Sassanid history, from Darmesteter to Christensen, to Nöldeke or Spuler, state that the royal family had been evacuated from the capital Ctesiphon well before the Arab invasion. Their account seem to agree with a number of islamic sources such as Maškur, II, pp. 1288 ff. and 1344 ff.; Ḥaṣuri.
However, other Islamic sources report the capture and reduction to slavery of a kin (not necessarily the daughter) of Emperor Yazdgerd III. The young Princess was supposedly captured in northern Khorasan, and is said to have been sent to the arab governor, who in turn have send her to the caliph.
Sources from the China of the T’ang dynasty (r. 618-907) regarding the Arab conquest of Persia, remain silent about an eventual captivity of one of the members of the family of Emperor Yazdgerd III (Marquart, pp. 68-69; Chavannes, pp. 171-73; Hoyland, pp. 243 ff.).
However, it is very likely that a Zoroastrian Sassanid Princess was captured, reduced to slavery and given in marriage to a noble-man or Imam of the arab conquerors. The fact that both sunni and shia accounts report a very similar story makes it much more plausible.
Interestingly, both sunni and shia accounts emphasize the ahl-e-kitab status (people of the book status) of the young Princess meaning Shahr-bánú has always stayed a Zoroastrian.
In the literary tradition, Shahr-bánú passes away by drowning in the Euphrates, after having witnessed the massacre of her family at Karbalā.
Popular belief decidedly preferred otherwise; the most recurrent version of the oral legend of the daughter of Emperor Yazdgerd III, here called Bibi (respectable Lady or grandmother) Šahrbānu: after the day of ʿĀšurāʾ Bibi Shahr-bánú is able to escape, as had predicted her husband, with Ḏu ʾl-Janāḥ, the horse of Imam Hussain.
Pursued by her terrifying enemies, she reaches up to the mountain at Ray, south of the mighty Alborz Mountains. Exhausted, and at the limits of her strength, all alone, she invokes God to be delivered from her assailants.
At this point, the mountain miraculously opens and offers refuge to the princess. The location became a sanctuary to the princess, a pilgrimage site to remain so until today (Šahidi, pp. 186 ff.).
An almost identical story is found to be at the source of the Zoroastrian sanctuary of Bānu Pārs (Lady of Persia), northwest of the plain of Yazd (Sorušiān, p. 204). More generally, themes such as the escape of Zoroastrian Persian nobles (often members of the royal family) from the arabs and their miraculous rescue by God thanks to elements of nature are frequently appear in legends of Zoroastrian sanctuaries in central mountain of Iran Persia (Sorušiān, pp. 205-11; Strack, I, pp. 119 and 227-28).
ardeshir
The above article and all the citations therein are taken entirely from Encyclopedia Iranica, my personal interjections and revisions are added in some places
Authentic Gatha Zoroastrianism 
History shows thatYazgerd III the Iranian emperor had no daughter He had only one child named Firooz who escaped to China after the Arab invasion, The story of Sharbanu is not true, invented by Muslims to deceive Iranians
Mr Mobarakeh, please cite all your historical sources and citations, Thnx
Please refer to Tarikh Iran Bastan 6th edition by Khodadaian Ancient Iran ,Sazeman Intesharat Ashrafi by MohammadJavad Mashkoor 1367 and Iranian History Pirnia.
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Strange how the story of a persian princess escaping from her captors and finally being engulfed in a mountain seems to wander with a life of its own. Here in Southern Brazil one of the oldest tales, from the time of the Jesuit Missiones, tells of a captive Princess, brought by the arabs from the “Land of the Mages” to the misterious land of Salamanca in Spain. After the Reconquista, these arabs take a ship to the New World to scape the christians, only to be met there by the Guarani red demon, Añangá-Pitã, who transforms the princess into a Teiniaguá (sort of gecko) and the sacred wand which she carried with her into a bright red ruby stone, which he then inserts in her head. The princess lives in this accursed state in a pond, until a native young man from Santo Tomé finds her and, seeing her true form at night, falls in love with her. The jesuit priests want to kill him for his sacrilege, but the princess prays to the Uruguay river for assistance and it cracks the earth, scaring the population and giving time for the princess to save the man. They protect themselves inside the hill of Jarau, which closes after their entrance. People used to visit the hill with gifts untill the end of the 19th century, but even today the story is told in schools here, where the couple is said to be the ancestors of the Gaucho people.
If you analise the components of this tale, there are lots of interesting details that seem to corroborate to an iranian influence. First, in every version the princess is from the “Land of the Magi” and in particular said to hold the “knowledge of the Magi Masters” with which she prays to the river for assistance in the climax of the story. Then, there’s the sacred wand, which seems to bring favour to the princess even when transformed into a ruby, since when the native man first finds her a bright light emanates from her face, where the ruby stands.
Saying that she willingly “married” an imam is a joke. Saying she had any choice by the compassionate ali is even worse. If she had any choice at all it was which master she had to serve. The poor girl was forced in to it. The dessimation of her people, culture, language, history is hardly romantic. Those culprits are far from her fantasies.
I pray for her at home and at pire sabz