In one of your answers regarding the Banu Quraiza,you write: “Because Sa`d ibn Mu`aaz’s decision was in accordance with the directives of the Torah, which the Jews accepted to be divine and were, therefore, subject to, the Prophet (pbuh) did not alter the decision”. I have a doubt regarding this.Why did Prophet(pbuh) judge the people of Banu Quraiza by Torah and not by the Quran? Because according to the Quran, Prophet(pbuh) should judge all the people including jews by Quran.
As should be clear from my earlier response, it was not the Prophet (pbuh), who decided about the punishment to be implemented upon the Banu Qurayzah. It was in fact Sa`d ibn Mu`aaz who, on the request of the Banu Qurayzah was made the arbitrator and given the authority to take this decision.
Thus, it was in fact the companion of the Prophet (pbuh) – Sa`d ibn Mu`aaz – who took the decision.
I hope this helps.