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." (RU)
English reference (RU): Vol. 3, Book 12, Hadith 2274 (RU)
Arabic reference (RU): Book 12, Hadith 2360 (RU)