Mishkat al-Masabih 3963
Abu Sa'id al-Khudri said:
When the B. Quraiza surrendered agreeing to have their fate decided by Sa‘d b. Mu'adh God’s Messenger sent for him and he came on an ass. When he drew near God's Messenger said, “Rise up in respect to your chief.” Then when he had come and sat down God's Messenger said, “These people have surrendered agreeing that you should decide their fate,” so he said, “I decide that the fighting men be killed and that the offspring be taken into captivity.” He then declared, “You have given regarding them the decision of the King.” A version has, “God’s decision.” 

(Bukhari and Muslim.)
وَعَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ قَالَ: لَمَّا نَزَلَتْ بَنُو قُرَيْظَةَ عَلَى حُكْمِ سَعْدِ بْنِ مُعَاذٍ بَعَثَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِليه فَجَاءَ عَلَى حِمَارٍ فَلَمَّا دَنَا قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «قُومُوا إِلَى سَيِّدِكُمْ» فَجَاءَ فَجَلَسَ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِنَّ هَؤُلَاءِ نَزَلُوا عَلَى حُكْمِكَ» . قَالَ: فَإِنِّي أَحْكُمُ أَنْ تَقْتُلَ الْمُقَاتِلَةُ وَأَنْ تُسْبَى الذُّرِّيَّةُ. قَالَ: «لَقَدْ حَكَمْتَ فِيهِمْ بحُكْمِ المَلِكِ» . وَفِي رِوَايَة: «بِحكم الله»