Sahih al-Bukhari 1905
Narrated 'Alqama:
While I was walking with `Abdullah he said, "We were in the company of the Prophet (ﷺ) and he said, 
'He who can afford to marry should marry, because it will help him refrain from looking at other 
women, and save his private parts from committing illegal sexual relation; and he who cannot afford 
to marry is advised to fast, as fasting will diminish his sexual power."
حَدَّثَنَا عَبْدَانُ، عَنْ أَبِي حَمْزَةَ، عَنِ الأَعْمَشِ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، قَالَ بَيْنَا أَنَا أَمْشِي، مَعَ عَبْدِ اللَّهِ ـ رضى الله عنه ـ فَقَالَ كُنَّا مَعَ النَّبِيِّ صلى الله عليه وسلم فَقَالَ ‏
"‏ مَنِ اسْتَطَاعَ الْبَاءَةَ فَلْيَتَزَوَّجْ، فَإِنَّهُ أَغَضُّ لِلْبَصَرِ وَأَحْصَنُ لِلْفَرْجِ، وَمَنْ لَمْ يَسْتَطِعْ فَعَلَيْهِ بِالصَّوْمِ، فَإِنَّهُ لَهُ وِجَاءٌ ‏"‏‏.‏