About the fate of Banu Quraythah
6-3-2013 | IslamWeb
Question:
Assalamu Alaikum, For my previous question regarding the fate of banu quraiza, you referred to a fatwa in which you said that Prophet ruled according to old testament and Allah approved the ruling. Since there would having many jewish teenagers who would not have been directly involved in the breach of the agreement and the conflict, please explain why Allah grant permission to the Prophet to make such ruling?.
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
What we meant in the Fatwa which we referred you to (i.e. Fatwa 99502) is that this ruling which Saa'd ibn Mu’aath 
issued and which the Prophet 
approved and told him about it: “You have indeed ruled according to the judgment of the King or according to the judgment of Allaah”, is that there is a ruling similar to it in the Torah. This was in response to those who deny Islam and raise some misconceptions about the issue of Banu Quraythah.
We have quoted the text from the Torah in this regard, however, this does not mean that the Prophet ruled according to the Torah. So, please read carefully what we have mentioned in that Fatwa.
As regards killing the fighters of Banu Quraythah, then you should know that the Prophet only killed those who had reached the age of puberty. As regards those who had not reached the age of puberty, the Prophet did not kill them. The adolescent is a child who is approaching puberty; so he has not yet reached puberty.
‘Atiyyah Al-Qurathi said: "I was with them on the day of (the battle of) Banu Quraythah, so the Prophet ordered that I would be checked whether I started to grow pubic hair, so they uncovered my pubes and found out that there was no hair on it, so they put me with the spoils (of war)?” [Abu Daawood and At-Tirmithi who graded it Hasan Saheeh]
Some scholars deduced from this that growing pubic hair is a sign of puberty.
It is well known that the Sharee’ah [Islamic Law] forbids the killing of people who do not deserve to be killed, like the elderly, women and children. So, if the Sharee’ah orders the killing of someone, then this is a proof that such a person deserves to be killed.
Allaah Knows best.