Juwariyya and Sayyifa: The Truth behind the Marriage with the Prophet The criticism of this marriage is that Prophet Muhamamd allegedly forced Juwariyya and Sayiffa (two different women) to marry him. This is absolutely false if we look at the evidence from authentic sources, the hadith (NOT Ibn Ishaq, Al-Waqidi or Al- Tabari). Prophet Muhammad's marriage with Juwariyya
The tribe Bani Mustaliq were preparing to launch an attack on the Muslims. The Muslims had foreknowledge about this, therefore they took the initiative and attacked first. The Bani Mustaliq were not aware that the Muslims knew about their preparation for war, therefore they were surprised as to why the Muslims attacked them.
It is alleged by some anti-Islamic writers that the Prophet Muhammad allowed the Muslim men to have sex with the women captives of Bani Mustaliq. However this is fabrication and a lie, which I already refuted here.
The Bani Mustaliq were allies with the Meccans. They hated Islam and wanted to bring it down-- they planned an attack on Prophet Muhammad and the Muslims.
Muhammad had received news that the tribe was gathering together against the Muslims under the leadership of al-Harith ibn Abu Dirar.tribe Banu Mustaliq was preparing to go launch an attack on Madinah, but the Muslims caught wind of their plan and quickly raised a defense force of 700 men who marched forward to the strategic point of Al-Marisa'. The Muslim army then sent a message to Banu Mustaliq to accept Islam, and in doing so abandon their hostilities and continue to live in peace and security in their own land. Instead of accepting this offer Banu Mustalaq declared war and shot one of the Muslim soldiers with an arrow, at which point wild fighting broke out.
After minimal casualties, the Muslim forces were victorious. Among the many captives was Juwayriya, whose husband, Mustafa bin Safwan, had been killed in the battle. She initially fell among the booty of Muhammad's companion Thabit b. Qays b. Al-Shammas. Troubled by this, Juwayriya sought a deed of redemption from Muhammad. Muhammad proposed to marry her and as a result freed her from the bondage of Thabit b. Qais and consequently ameliorated the condition of her captured tribe.
The account is recorded in the hadith:
Narrated Aisha, Ummul Mu'minin:Juwayriyyah, daughter of al-Harith ibn al-Mustaliq, fell to the lot of Thabit ibn Qays ibn Shammas, or to her cousin. She entered into an agreement to purchase her freedom. She was a very beautiful woman, most attractive to the eye.
Aisha said: She then came to the Apostle of Allah (peace_be_upon_him) asking him for the purchase of her freedom. When she was standing at the door, I looked at her with disapproval. I realised that the Apostle of Allah (peace_be_upon_him) would look at her in the same way that I had looked.
She said: Apostle of Allah, I am Juwayriyyah, daughter of al-Harith, and something has happened to me, which is not hidden from you. I have fallen to the lot of Thabit ibn Qays ibn Shammas, and I have entered into an agreement to purchase of my freedom. I have come to you to seek assistance for the purchase of my freedom.
The Apostle of Allah (peace_be_upon_him) said: Are you inclined to that which is better? She asked: What is that, Apostle of Allah? He replied: I shall pay the price of your freedom on your behalf, and I shall marry you.
She said: I shall do this. She (Aisha) said: The people then heard that the Apostle of Allah (peace_be_upon_him) had married Juwayriyyah. They released the captives in their possession and set them free, and said: They are the relatives of the Apostle of Allah (peace_be_upon_him) by marriage. We did not see any woman greater than Juwayriyyah who brought blessings to her people. One hundred families of Banu al-Mustaliq were set free on account of her. (Sunan Abu Dawud, Book 29, Number 3920)
Notice that Juwayriyah said that she had already bargained to purchase her freedom. She asked the Prophet who then offered her marriage and she agreed WILLINGLY. However, she could have refused because if she really wanted to, she could have waited for her family members to come and pay her ransom since she was well known amongst her tribe.
So we can see that Juwayriyah was given a choice to stay with her family or be married to Prophet Muhammad:
It was also reported that Juwayriyah's father said, "O Muhammad! My daughter was captured and this is her ransom. Such a noble lady should never be captured, so set her free." the Prophet (peace be upon him) said, "Do you not think it is better if we let her make the decision herself (whether to go or to stay)?" Al-Harith answered in the affirmative. When he came to inform Juwayriyah of it, she replied, "I accept Allah and His Messenger." 
The marriage was a huge blessing as one hundred familes were released from captivity because Juwayriyya was freed and married by the Prophet. Some time later her father and all the men of her tribe who had been freed also accepted Islam as their religion.Juwayriyya was described as being very beautiful and being very pious. She is also described as spending most of her time in prayer.
Prophet Muhammad's marriage with Sayiffa
Sayiffa bint Huyayy ibn Akthab was a Jewish Woman of the Bani Nadir tribe of the Jews. She also was described as being very beautiful and devout.
There were three powerful Jewish Tribes in Madinah. The first thing Prophet Muhammad did when he came to Madinah was sign a treaty with the Jews. However all three
Jewish tribes broke the treaty (more on this later).
As for Sayiffa and the Prophet Muhammad’s marriage to her, it should be remembered that Sayiffa actually had a dream before meeting the Prophet the she would be married to him:
She was married off to Sallam b. Mishkam, who later divorced her.  Saffiya is said to have informed Kinana (her ex-husband) of a dream she had in which the moon had fallen from the heavens into her lap. Kinana interpreted it as a desire to marry Muhammad and struck her, leaving a mark which was still visible when she first had contact with Muhammad.
As Orenitalist William Muir states:
"It is related that she bore the mark of a bruise upon her eye; when the Prophet asked her tenderly the cause, she told him that, being yet Kināna's bride, she saw in a dream as if the moon had fallen from the heavens into her lap; and that when she told it to Kināna, he struck her violently, saying: 'What is this thy dream but that thou covetest the new king of the Ḥijāz, the Prophet, for thy husband!' The mark of the blow was the same which Moḥammad saw." 
So it was already prophcized that she would be married to Prophet Muhammad.
Her father and brother went from Khaybar to join the Meccan and Bedouin forces besieging Prophet Muhammad in Medina during the Battle of the Trench. When the Meccans withdrew Muhammad besieged the Banu Qurayza. Sad a leader of a tribe determined that the Men of the Banu Qurayza should be killed and their women and children be made to slavery. In the ensuing massacre both Huyayy and his son (Sayiffa's brother) were killed by the Muslims, together with all the men of the Banu Qurayza (more on this later)
After the battles of Khaybar--- The Muslims defeated several Jews from their tribes. Kinana ibn al-Rabi (Sayiffa's former husband) was killed by Bin Maslama for killing Maslama's brother, Mahmood. However the story of Kinana ibn al-Rabi being tortured for money under the orders of the Prophet are false.
Female captives were then given to Prophet Muhammad and the Muslims. Among them was Safiyya. Safiyya was assigned to Dihya ibn Khalifa. Prophet Muhammad
then gave seven female captives to Dihya and gave Safiyya a choice. Either she could be his wife or she could be stay a Jew and go back to her tribe.
And as Martin Lings says: He [the Prophet Muhammad - Ed.] then told Safiyyah that he was prepared to set her free, and he offered her the choice between remaining a Jewess and returning to her people or entering Islam and becoming his wife. “I choose God and His Messenger,” she said; and they were married at the first halt on the homeward march. 
So Sayiffya wanted to get married to Prophet Muhammad—instead of going back to her family. The following can be shown by these hadith:
Narrated Anas: The Prophet stayed for three rights between Khaibar and Medina and was married to Safiya. ( Bukhari Volume 5, Book 59, Number 524)
Narrated Anas bin Malik: We arrived at Khaibar, and when Allah helped His Apostle to open the fort, the beauty of Safiya bint Huyai bin Akhtaq whose husband had been killed while she was a bride, was mentioned to Allah's Apostle. The Prophet selected her for himself, and set out with her, and when we reached a place called Sidd-as-Sahba,' Safiya became clean from her menses then Allah's Apostle married her. Hais (i.e. an 'Arabian dish) was prepared on a small leather mat. Then the Prophet said to me, "I invite the people around you." So that was the marriage banquet of the Prophet and Safiya. Then we proceeded towards Medina, and I saw the Prophet, making for her a kind of cushion with his cloak behind him (on his camel). He then sat beside his camel and put his knee for Safiya to put her foot on, in order to ride (on the camel). (Bukhari Volume 5, Book 59, Number 522)
So both Juwayriyya and Safiyya were widows. Scholars believe that Muhammad married Safiyya as part of reconciliation with the Jewish tribe and as a gesture of goodwill. 
As for the false story of Kinanna, the ex-husband of Juwayriyya being tortured by the Prophet with fire because he hid some money, I have shown that the story is completely false here. It is also alleged that there were treasures found at the conquest of Khaibar. This is absolutely false—in fact there was so little food with the Muslims that the Muslims had to bring their own food to the Wedding between the Prophet and Juwayriyaa. The Prophets wives had the freedom to leave...
What about the Prophet Muhammad’s wives? Were they forced to stay with Prophet Muhammad? Were they forced to be his wives forever? The answer is no, the wives of the Prophet could leave whenever they wanted according to both the Quran and the HadithThe Prophets wives had the freedom to leave:
O Prophet! Say to thy Consorts: "If it be that ye desire the life of this World, and its glitter,- then come! I will provide for your enjoyment and set you free in a handsome manner. But if ye seek Allah and His Messenger, and the Home of the Hereafter, verily Allah has prepared for the well-doers amongst you a great reward. (Quran 33:27-28)
'A'isha (Allah be pleased with her) reported: Allah's Messenger (may peace be upon him) gave us (his wives) the option (to get divorce) and we chose him and he did not count it a divorce. (Muslim Book 009, Number 3503)
'A'isha (Allah be pleased with her) reported: Allah's Messeinger (may peace be upon him) gave us the option (to get divorce), but me made a choice of him and he did not count anything (as divorce) in regard to us. (Muslim Book 009, Number 3504)
May Allah bless the Prophet and his family. Ameen.
 Vacca, V. "Safiyya". in P.J. Bearman, Th. Bianquis, C.E. Bosworth, E. van Donzel and W.P. Heinrichs. Encyclopaedia of Islam Online. Brill Academic Publishers. ISSN 1573-3912.
 Muir (1912) pg. pp. 378-379
 (Ibn Hajar, Al-Isabah, vol. 4, p.265, Cited in Muhammad Fathi Mus'ad, The Wives of the Prophet Muhammad: Their Strives and Their Lives, p.151)
The above narration has been authenticated by Ibn Hajar in Tahzheeb al Tahzheeb, vol. 12, no. 407.
 Martin Lings, Muhammad: His Life Based On The Earliest Sources (George Allen & Unwin, 1983), p. 269
 Nomani(1970) p. 424 and Watt (1964) p. 195