Jami` at-Tirmidhi 1584

Narrated 'Atiyyah Al-Qurazi: "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." [Abu 'Eisa said:] 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