Traitors or Betrayed?
When Mohammed first entered Yathrib (Al-Madina Al-Munawwarah), he was counting on the support of its people. One particular ethnic group he thought would give more authority to his prophethood were the Jews because they had the Torah and all the previous Prophets were Jewish.
The Jews were many in Yathrib and its suburbs. There were the Bani Al-Nadheer Jews, the Bani Qaynuqa' Jews, the Bani Quraytha Jews, and several more. The Jews were rich and successful in their businesses. A great asset to the young Islamic Nation.
At first, Mohammed was trying to befriend the Jews and get them on his side. He insisted that the People of the Book (Jews and Christians) worship the same God [Quran Surah 29:46]. He said that the same God sent down the Torah [Quran Surah 5:48]. He ordered the Muslims to fast Aashoora' or the Passover [Saheeh Bukhari - 2004]. Even the Qibla (the direction the Muslims face in prayer) was towards Jerusalem - the same direction the Jews faced in prayer [Saheeh Bukhari - 41].
But no matter how hard Mohammed tried to convince them that he is a prophet he just couldn't. Once he even barged into a Jewish Synagogue in Yathrib (Al-Madina Al-Munawwarah) and said that if only twelve Jews would believe in him then Allah would spare them his wrath [Musnad Ahmad - 23464].
When he realized that the Jews wouldn't believe in him, and that their unbelief would turn against him, because they have the Torah which has the criteria for any prophet, he realized that they should be eliminated. So at first he switched the Qibla (the direction the Muslims face in prayer) from Jerusalem to Mecca [Quran Surah 2:144 and Saheeh Bukhari - 41]. Then warned them; they either become Muslims and be safe, or sell their possessions and leave their land [Saheeh Muslim - 1765 & 1767 and Sunan Abi Dawood - 3003].
Mohammed marched towards the Jews in order to either exile them or make a treaty with them. The Bani Al-Nadheer Jews refused to make a treaty with Mohammed so they fought against him, lost, and subsequently were exiled. The Bani Quraytha Jews saw the fate of their Bani Al-Nadheer brethren so they had no choice but to make a peace treaty with him [Saheeh Muslim - 1766 and Sunan Abi Dawood - 3004].
Yet Mohammed was determined that all Jews should be either exiled or killed - he was set on their elimination. He cannot simply break the treaty with Bani Quraytha though because it would be bad for his image as a Prophet who's supposed to keep his promises and treaties. He strongly emphasized the importance of keeping treaties [Quran Surah 9:4 and Saheeh Bukhari - 33]. So his only way out was to make it appear as though Bani Quraytha were the ones who broke the treaty.
Ghazwat Al-Khandaq (The Battle of the Trench or Ditch) came. The Pagan Arab tribes retreated and Mohammed was ready for battle. Mohammed went to the Bani Quraytha Jews and eliminated them because it was claimed that they betrayed the Muslims and renounced the treaty, but did they?
The Battle of Al-Khandaq (Trench) and The Battle of Bani Quraytha
Quraysh and Ghatfan, encouraged by the exiled Bani Al-Nadheer Jews, wanted to eliminate Mohammed once and for all. They gathered up a great army and put Yathrib under siege [Saheeh Bukhari - 4103]. Mohammed , based on a suggestion by Salman Al-Farisi, dug a trench around Yathrib [Saheeh Bukhari - 2837], except for the Bani Quraytha side that is, because they had great fortresses and it would be practically impossible for the Pagan Arabs to get through their fortresses unless Bani Quraytha allowed it. Now since Mohammed and Bani Quraytha had a treaty, Mohammed had nothing to fear [Saheeh Muslim - 1766 and Sunan Abi Dawood - 3004]. Thus all was set.
Now the siege has started, Mohammed was running low on food and resources [Saheeh Bukhari - 4101 and Musnad Ahmad - 13808], his companions were terrified [Saheeh Bukhari - 4103 and Musnad Ahmad - 10613], and above all that it was rumored that Bani Quraytha were going to break the treaty between them and Mohammed and let the Pagan Arabs come through their side. But after a while, a sandstorm hit the armies of the Pagan Arabs, and since Bani Quraytha refused to let them in through their fortresses, the armies had no choice but to retreat [Musnad Ahmad - 22823].
Mohammed on the other hand was ready for battle, he had a full army equipped and eager to fight in the name of Allah. The rumors that Bani Quraytha wanted to betray him were his only excuse, that and an order sent from Allah via Jibreel (Gabriel). He went to them, put them under siege for 14 days. Finally they surrendered. So Mohammed killed all their men, enslaved their women and children [Saheeh Muslim - 1769]. Now there was one less Jewish tribe to worry about.
Traitors or Betrayed?
Now it all comes down to this; are the Bani Quraytha Jews traitors or were they betrayed?
First of all, how do we know if a treaty is broken? We cannot simply assume that a treaty is broken because of mere rumors [Quran Surah 49:12]. We can only assume that a treaty is broken if:-
1. The other side officially renounces the treaty
2. The other side does an action which is a direct violation of the treaty
Does any one of the former apply to the Bani Quraytha Jews?
I've searched the nine books of Hadeeth (Saheeh Bukhari, Saheeh Muslim, Sunan Al-Tarmithi, Sunan Al-Nasa'i, Sunan Abi Dawood, Sunan Ibn Majah, Musnad Ahmad, Muwatta' Malik, and Sunan Al-Darimi). In my search I did not find any single Hadeeth which indicates that Bani Quraytha either officially (or even unofficially) renounced the treaty, nor did I find a Hadeeth which indicates that Bani Quraytha violated the treaty in any way.
As a matter of fact, the only Hadeeth I found regarding Bani Quraytha's position was one Hadeeth [Musnad Ahmad - 22823] which says that Bani Quraytha actually refused to assist the Pagan Arabs in any way in their assault against Mohammed.
We saw how much Mohammed wanted to get the Jews on his side, but since he couldn't he had to eliminate them. We saw that the Bani Quraytha Jews actually refused to aid the Pagan Arabs or even let them in through their fortresses. Yet Mohammed was determined to eliminate all non-Muslims from Arabia. The Jews were innocent yet that didn't stop him, he marched to Bani Quraytha and ruthlessly slaughtered all their men, enslaved their women and children. He violated the treaty himself, and he was the one who always preached how treaties should be kept.
History is written by the victors, thus the Muslims have throughout history claimed that the Bani Quraytha Jews were the traitors. Yet because the nine Hadeeth collectors (From Bukhari to Al-Darimi) were men who feared Allah, they couldn't include in their books any Hadeeth which wasn't authentic, thus they couldn't find any Hadeeth to put in their books which talks about the treachery of Bani Quraytha.
It all comes down to this, does a true Prophet of God break his treaties?