Hadith: Those who can afford marriage should marry, for it is more effective in lowering the gaze and guarding chastity. He who cannot afford it should fast, for indeed it serves as a restraint for him

عَن عَبْدِ اللَّهِ بنِ مَسْعُودٍ رَضِيَ اللَّهُ عَنْهُ قَالَ: كُنَّا مَعَ النَّبِيِّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ، فَقَالَ:
«مَنِ اسْتَطَاعَ البَاءَةَ فَلْيَتَزَوَّجْ، فَإِنَّهُ أَغَضُّ لِلْبَصَرِ، وَأَحْصَنُ لِلْفَرْجِ، وَمَنْ لَمْ يَسْتَطِعْ فَعَلَيْهِ بِالصَّوْمِ، فَإِنَّهُ لَهُ وِجَاءٌ».
[صحيح] - [متفق عليه] - [صحيح البخاري: 1905]

‘Abdullāh ibn Mas‘ūd (may Allah be pleased with him) reported: We were in the company of the Prophet (may Allah's peace and blessings be upon him), and he said:
"Those who can afford marriage should marry, for it is more effective in lowering the gaze and guarding chastity. He who cannot afford it should fast, for indeed it serves as a restraint for him."
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 1905]

Explanation

The Prophet (may Allah's peace and blessings be upon him) urged those who are able to have sexual intercourse and afford the expenses of marriage to marry, as it protects their sight from what is forbidden, keeps their private parts more chaste, and prevents them from falling into immorality. As for those who cannot afford the expenses of marriage yet can have sexual intercourse, they should observe fast, as it undermines the desire of the private parts and stops the evil of semen.