جامع الترمذي

Narrated Samurah bin Jundab:

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.

[Abu 'Eisa said:] This Hadith is Hasan Sahih.

Hajjaj bin Artah narrated similarly from Qatadah.