Mujahid (may Allah have mercy on him) said: I heard a man in the mosque of Kufah saying: "On the day Sa'd bin Mu'adh (may Allah be pleased with him) gave his judgement concerning Banu Qurayzah, I was a boy. They were in doubt about me, and they found that the razor had not passed over me (that is, hair had not yet grown), so I was kept alive."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14511