مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3626
Musnad of Abdullah bin Mas'ood
It was narrated that Ibn Mas’ood (رضي الله عنه) said: We used to go on campaigns with the Messenger of Allah (ﷺ) and we had no wives with us. We said: O Messenger of Allah, can we not castrate ourselves? But he forbade us to do that.
Musnad Ahmad 3650Its isnad is saheeh, al-Bukhari (5071) and Mustim (1404)]