From here they adduced: One who lends on interest is guilty of five transgressions: "You shall not give," "You shall not take," "You shall not impose interest upon him," "You shall not be as a creditor to him," (Leviticus 19:14) "You shall not place a stumbling block before the blind man." Just as the lender and the borrower transgress, so, the guarantor, the witnesses, and the scribe. R. Meir excludes the scribe.
Here They Adduced One Who Lends on Interest Is Guilty
Mekhilta Tractate Kaspa 1:9