(3) باب مَنْ لَمْ يَسْتَطِعِ الْبَاءَةَ فَلْيَصُمْ
Narrated `Abdullah:
We were with the Prophet (ﷺ) while we were young and had no wealth whatever. So Allah's Messenger (ﷺ) said, "O young people! Whoever among you can marry, should marry, because it helps him lower his gaze and guard his modesty (i.e. his private parts from committing illegal sexual intercourse etc.), and whoever is not able to marry, should fast, as fasting diminishes his sexual power."
Reference: Sahih al-Bukhari 5066
In-book reference: Book 67, Hadith 4
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 7, Book 62, Hadith 4