مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3997
Musnad of Abdullah bin Mas'ood
It was narrated that 'Abdur-Rahman bin Yazeed said: 'Abdullah said: We were with The Messenger of Allah (ﷺ), young men who had nothing. And he said: “O young men, whoever among you can afford it, let him get married, for it is more effective in lowering the gaze and guarding one's chastity. And whoever cannot afford it should fast, for it will be a shield for him."
Musnad Ahmad 4023Its isnad is saheeh, al-Bukhari (5066) and Muslim (1400)]