Is it really?
“Then they [the Jewish Qurayzah tribe] surrendered, and the apostle [Muhammad] confined them in Medina in the quarter of d. al-Harith, a woman of B. Al-Najjar. Then the apostle went out to the market of Medina (which is still its market today) and dug trenches in it. Then he sent for them and struck off their heads in those trenches as they were brought out to him in batches. Among them was the enemy of Allah Huyayy b. Akhtab and Ka’b b. Asad their chief. There were 600 or 700 in all, though some put the figure as high as 800 or 900.” — Ibn Ishaq 690
Islamic apologists in the West like to claim that Ibn Ishaq, Muhammad’s earliest biographer, is unreliable. But the hadith collection Sahih Bukhari is the one that Sunni Muslims consider most reliable, and it has this:
Bani An-Nadir and Bani Quraiza fought (against the Prophet, violating their peace treaty), so the Prophet exiled Bani An-Nadir and allowed Bani Quraiza to remain at their places (in Medina) taking nothing from them till they fought against the Prophet again. He then killed their men and distributed their women, children and property among the Muslims, but some of them came to the Prophet and he granted them safety, and they embraced Islam. He exiled all the Jews from Medina. They were the Jews of Bani Qainuqa’, the tribe of `Abdullah bin Salam and the Jews of Bani Haritha and all the other Jews of Medina. (Sahih Bukhari vol. 64, no. 4028)
There are also traces of this story in other hadiths that Muslims consider reliable. (According to Ibn Ishaq, Sad bin Muadh was chosen by Muhammad to pronounce sentence on the Banu Qurayzah Jews, and he declared that they should be executed.)
Narrated by Abu Said Al-Khudri: Some people (i.e. the Jews of Bani bin Quraiza) agreed to accept the verdict of Sad bin Muadh so the Prophet sent for him (i.e. Sad bin Muadh). He came riding a donkey, and when he approached the Mosque, the Prophet said, “Get up for the best amongst you.” or said, “Get up for your chief.” Then the Prophet said, “O Sad! These people have agreed to accept your verdict.” Sad said, “I judge that their warriors should be killed and their children and women should be taken as captives.” The Prophet said, “You have given a judgment similar to Allah’s Judgment (or the King’s judgment). (Sahih Bukhari vol. 5, no. 148)
And: “Narrated Atiyyah al-Qurazi: I was among the captives of Banu Qurayza. They (the Companions) examined us, and those who had begun to grow hair (pubes) were killed, and those who had not were not killed. I was among those who had not grown hair. (Sunan Abu Dawood 38:4390)
Also, some Muslims know this story and don’t think of it as a fabrication. A Taliban spokesman, Muhammad Khorasani, justified the Peshawar jihad massacre by likening it to Muhammad’s massacre of the Qurayzah tribe. And an Islamic State jihadi justified massacres by invoking Muhammad, who “slaughtered 700 people.”
“Iranian Sheikh Sadiq Akhvan: Massacre of Jewish Banu Qurayza Tribe Is a Holocaust-Like Fabrication by the Jews,” MEMRI, November 17, 2018:
Iranian Sheikh Sadiq Akhvan said that no story has led Islamic scholars and historians into a trap laid by the Jews as much as the story of the massacre of the Jewish tribe of Banu Qurayza in Medina, which he said is “another Holocaust-like lie.” He said that the Jews are infamous for fabricating myths. Sheikh Akhvan added that the Jews should have established Israel in Germany or Britain instead of Palestine. His remarks aired on Al-Kawthar TV (Iran) on November 17, 2018.
Following are excerpts:
Sheikh Sadiq Akhvan: No story has led scholars of Islam, of hadith, or of history into a trap laid by the Jews as much as the lie about the Banu Qurayza [massacre] has. My dear sisters and brothers, you all know what the Jews are like. I am not addressing only the Muslims. Even the Christians and others know that the Jews are infamous worldwide for inventing myths and distorting facts. This lie was not the first in their history, nor was it the last.
[…]
You have all seen that under the pretext of the great Holocaust that took place during WWII, the Jews came and occupied Palestine. They even gained international legitimacy. Why? Because they said: “We are miserable. Three million of us, more or less, were burned in Hitler’s furnaces.” Go to Germany or to Britain and establish your Israel there. How is this the fault of the Arabs and the Muslims? Palestine is 100% an Arab and Islamic land. We see that the lie about the Banu Qurayza [massacre], which dates back to the advent of Islam, is another Holocaust-like lie.