Sunan Ibn Majah, Hadith 2274 ⓘ
It was narrated from Abu Hurairah that the Messenger of Allah said: "There are seventy degrees of usury, the least of which is equivalent to a man having intercourse with his mother."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ سَعِيدٍ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ إِدْرِيسَ، عَنْ أَبِي مَعْشَرٍ، عَنْ سَعِيدٍ الْمَقْبُرِيِّ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " الرِّبَا سَبْعُونَ حُوبًا أَيْسَرُهَا أَنْ يَنْكِحَ الرَّجُلُ أُمَّهُ " .
also referenced under: Book 12, Hadith 2360 (In-Book) & Volume 3, Book 12, Hadith 2274 (DarusSalam)