Re: need to know for the sake of knowledge
At one time there were three girls living in the household of Khadija. Their names were Zainab, Ruqayya and Umm Kulthoom. Zainab, the eldest of the three, was married to one Abul-‘As ibn er-Rabi’ of Makkah. This man fought against the Prophet in the battle of Badr, and was captured by the Muslims. To ransom his freedom, his wife sent to the Prophet, a necklace which at one time had belonged to Khadija, and she had given it to her as a present on her marriage. Abul-'As was set free; he returned to Makkah, and sent Zainab to Medina as he had promised to do. Zainab, however, died soon after her arrival in Medina. Later, Abul-'As also went to Medina, accepted Islam, and lived with the Muslims.
The other two girls, Ruqayya and Umm Kulthoom, were married to Utba and Utaiba, the sons of Abu Lahab and Umm Jameel. Umm Jameel was the sister of Abu Sufyan, the chief of the clan of Umayya. Abu Sufyan, therefore, was the maternal uncle of Utba and Utaiba.
It is not known with any degree of certainty who were these three girls. Most of the Sunni historians claim that they were the daughters of Muhammad and Khadija. According to some other historians, they were the daughters of Khadija by an earlier marriage.
The Shia Muslims disagree. They assert that Zainab, Ruqayya and Umm Kulthoom were not the daughters of Muhammad and Khadija; in fact, they were not even the daughters of Khadija by any earlier marriage; they were the daughters of a (widowed) sister of Khadija. Khadija’s sister also died, and upon her death, she brought the three girls into her own house and brought them up as her own children.
According to the Shia Muslims, Muhammad and Khadija had three and not six children.The first two of them – Qasim and Tayyeb or Tahir – were boys, and both of them died in their infancy. Their third and the last child was a girl – Fatima Zahra. She was their only child who did not die in infancy.
The girls – Zainab, Ruqayya and Umm Kulthoom – could not have been the daughters of the Prophet of Islam. If they were, he would not have given them in marriage to the idolaters which the husbands of all three of them were. It’s true that all three girls were married long before the dawn of Islam. But then he did not violate any of the imperatives of Qur’an at any time – before or after he was ordained God’s Messenger. And Qur’an is explicit on the prohibition of the marriage of a Muslim woman to a pagan.
The proscription of the marriage of a Muslim woman and a polytheist occurs in the following verses of Qur’an:
Do not marry (your girls) to unbelievers. (Chapter 2; verse 221)
They (believing women) are not lawful (wives) for the unbelievers, nor are the (unbelievers) lawful (husbands) for them. (Chapter 60; verse 10)
There are other verses in Qur’an which, without referring specifically to marriage, make it impossible for a Muslim to give his daughter or daughters to an idolater. Some of them are:
…the curse of God is on those without faith. (Chapter 2; verse 89)
…God is an enemy to those who reject faith. (Chapter 2, verse 98)
O ye who believe! Truly the pagans are unclean. (Chapyrt 9:verse 28)
Can a Muslim, even if he is a “marginal” or a “statistical” Muslim, believe that Muhammad, the Bringer and the Interpreter of Qur’an, would give his daughters to those men whom God has cursed; whose enemy He is; and who are unclean?
To a believer, the verses of Qur’an quoted above, are incontrovertible proof that Zainab, Ruqayya and Umm Kulthoom, all three married, at one time, to three idolaters in Makkah, were not the daughters of Muhammad Mustafa and Khadija.
It should also be noted that the Apostle who was very fond of children, never said anything about Zainab, Ruqayya and Umm Kulthoom. The parents give the same love to all their children, and do not make any distinction between them. But he was bestowing encomiums only upon his daughter, Fatima Zahra. Judging by the traditions, he was not even aware that three women called Zainab, Ruqayya and Umm Kulthoom existed.
Ruqayya and Umm Kulthoom were still living with their husbands when a new revelation, the Chapter 111 of Qur’an, came from Heaven. In this chapter Abu Lahab and his wife, Umm Jameel, the in-laws of Ruqayya and Umm Kulthoom, were cursed for their perversity.
The new revelation roused the anger of the old couple, and they ordered their sons to divorce their wives, and to send them back to Khadija’s home. The boys obeyed their parents, divorced their wives and they (the wives) returned to Khadija’s home. Sometime later, Ruqayya was married to Uthman bin Affan. She died in A.D. 624. After her death, her sister, Umm Kulthoom, was also married to Uthman. She died a few years later.
The years in Makkah, after the proclamation of Islam, and the early years in Medina, were fraught with peril for Muhammad. Everyday brought new challenges to him. He put his life in the line of fire as soon as he stepped out of his house. And yet, Ruqayya and Umm Kulthoom are never mentioned as giving any service to their father. On the other hand, Fatima Zahra helped her father in various emergencies, both in Makkah and Medina. Ruqayya and Umm Kulthoom both were many years older than Fatima, and they ought to have cheered and comforted their father whenever he was oppressed by the idolaters in Makkah or was wounded in battles in Medina but they never did.
The Sunni historians have bestowed upon Uthman the g*****loquent title of Dhun-Noorayn which means “the owner of two lights,” because he married, according to them, two daughters of the Prophet, an honor not attained even by Abu Bakr and Umar!
Uthman became the owner of two lights after marrying Ruqayya and Umm Kulthoom. But both of these girls were married to two idolaters, i.e., Utba and Utaiba, the sons of Abu Lahab, before they were married to Uthman. Therefore, each of the two sons of Abu Lahab ought to be called Dhun-Noor – the owner of one light. Each of them, Utba and Utaiba, was the owner of one light which he passed on to Uthman, thus making him the owner of two lights. After all, the lights remained the same; only the ownership changed!
from: http://www.al-islam.org/restatement/58.htm
who was son of Hazrat Hala :RA:. Hazrat Hala :RA: is sister of Hazrat Khajida 
wed locked Hazrat Ruqaiya