It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said:
"There are seventy degrees of usury, the least of which is equivalent to a man having intercourse with his mother." (FR)
English reference (FR): Vol. 3, Book 12, Hadith 2274 (FR)
Arabic reference (FR): Book 12, Hadith 2360 (FR)