بُلُوغُ الْمَرَامِ
Bulugh al-Maram 831
Business Transactions
وَعَنْ عَبْدِ اَللَّهِ بْنِ مَسْعُودٍ - رضى الله عنه - عَنْ اَلنَّبِيِّ - صلى الله عليه وسلم -قَالَ: { اَلرِّبَا ثَلَاثَةٌ وَسَبْعُونَ بَابًا أَيْسَرُهَا مِثْلُ أَنْ يَنْكِحَ اَلرَّجُلُ أُمَّهُ, وَإِنَّ أَرْبَى اَلرِّبَا عِرْضُ اَلرَّجُلِ اَلْمُسْلِمِ } رَوَاهُ اِبْنُ مَاجَهْ مُخْتَصَراً, وَالْحَاكِمُ بِتَمَامِهِ وَصَحَّحَهُ [1] .
Narrated 'Abdullah bin Mas'ud (RA): The Prophet (ﷺ) said: "Usury has seventy-three categories, the least one in sin is as that of a man who marries (has sexual relations with) his mother, and the very essence of usury is the (violation of the) honor of a Muslim man." [Ibn Majah reported it in a short form and al-Hakim in a complete one. The latter also graded it Sahih (authentic)].
Sunnah.com reference: Book 7, Hadith 64