That the Messenger of Allah (ﷺ) said: "Kill the elder men among the idolaters and spare the Sharkh amont them."

And the Sharkh are the boys who did not begin to grow pubic hair.

This Hadith is Hasan Sahih.

Hajjaj bin Artah narrated similarly from Qatadah.
Jami` at-Tirmidhi Book 21, Hadith 45
← Previous Hadith "On the day of (the battle of) Al-Ahzab, Sa'd bin Mu'adh was struck by an arrow such that the upper vein or lower vein of his forearm was severed. So the Messenger of Allah (ﷺ) tried to stop it with fire, but it made his arm bleed profusely so he left it. Then he did it another time but it caused it to bleed profusely. Upon seeing that he said: 'O Allah! Do not allow my soul depart until my eyes are comforted by elimination of Banu Quraizah.' He pressed his vein closed and it did not bleed a drop before they surrendered to the arbitration of Sa'd bin Mu'adh. He (the Prophet (ﷺ)) sent to him (Sa'd) who judged that their men should be killed, their women should be spared, and that the Muslims may share them among themselves. With this, the Messenger of Allah (ﷺ) said: 'You have judged according to Allah's judgement for them.' And they were four hundred. Then when he finished killing them, his vein opened up and he died."

There are narrations on this topic from Abu Sa'eed and 'Atiyyah Al-Qurazi.

This Hadith is Hasan Sahih.

Jami` at-Tirmidhi Book 21, Hadith 44 Next Hadith → "We were presented to the Messenger of Allah (ﷺ) on the day of (the battle of) Quraizah. Whoever had pubic hair was killed and whoever did not was left to his way. I was of those who did not have pubic hair so I was left to my way."

This Hadith is Hasan Sahih. This is acted upon according to some of the people of knowledge. They consider pubic hair an indication of the age of responsibility, if it is not known whether he has had a wet dream, or his age. This is the view of Ahmad and Ishaq.

Jami` at-Tirmidhi Book 21, Hadith 46