Prophet Muhammad (peace be upon him) did not order the execution of 800 Jews.
This claim is false and has no basis.
After the migration of Muslims from Mecca to Medina, Prophet Muhammad (peace be upon him), who was chosen by the majority as the head of state of Medinah, made the Charter of Medina (first-ever constitution). The Jews agreed to abide by this charter by which both Muslims and Jews were to defend Medinah in case of an invasion/attack on Madinah.
This historical event occurred after the largest battle took place in Medina during Prophet Muhammad’s life. Banu Qurayza (a Jewish tribe living in Medina) committed a treasonous act as they sided with the enemy right as the war broke out which led Muslims to the verge of annihilation.
After the threat to Medina was averted, Prophet Muhammad (peace be upon him) allowed the Jews to refer the matter to an arbitrator who was of their own choosing.
Sa’ad ibn Muadh (leader of their former allies, the Aus), whom they chose as an arbitrator declared this case of high treason to be an unpardonable offense and he passed down the decision based on the punishment prescribed by the Torah, not the Holy Quran, for treason.
Prophet Muhammad was merely a party in this case. It is false to accuse him of passing orders to kill anyone.
Rather he was willing to forgive them, and history stands witness to the fact that the Jews admitted themselves that they would’ve been forgiven for their treacherous act had they accepted Prophet Muhammad (peace be upon him) to be the arbitrator