In Romans 12:19, who says, 'Vengeance is mine; I will repay'?

Answer: The Lord

Do not avenge yourselves, but leave room for God's wrath. For it is written: 'Vengeance is Mine; I will repay, says the Lord.'

“Do not avenge yourselves, beloved, but leave room for God’s wrath. For it is written: “Vengeance is Mine; I will repay, says the Lord.””— Romans 12:19 (BSB)