Ibn Ezra on Leviticus 5:16

ישלם. וישלם אשר חטא מן הקדש עם תוס׳‎ חמישתו וזה הוא אשם בשגגה בתחלה ואחר כך ידע: HE SHALL MAKE RESTITUTION. He shall make restitution for sinning by using a holy object and add a fifth.³⁴A fifth of its value. This is a guilt offering brought by one who errs at first and then becomes cognizant of his sin.