Tafsiran Imamat 5:24: Rashi, Rashbam, Rabbeinu Bahya & Siftei Chakhamim

בראשו — This means the principal — the capital (ראש) money.

ביום אשמתו, when he confessed and promised not to sin again in respect to any or several of the above mentioned offences, i.e. denial of things given to him in trust, open robbery, abusing his position of authority unfairly, or appropriating things lost by another Jew when he was aware of the owner of the item in question.

לאשר הוא לו יתננו, “he shall give it to its owner.” This means that the party who had first been guilty of denial has to give both principal and premium to the injured party. Restitution is not effected through the good offices of the court but directly by the guilty party to the injured party. It is also possible that the words לאשר הוא לו mean that the money is to be returned to the party entitled to it, i.e. the heirs of the person from whom it has been taken against his will, if that person had died in the interval.

וחמשתיו [AND HE SHALL ADD] THE FIFTH PART [MORE THERETO) — By using the plural וחמשתיו the Torah includes in this law of restitution the many additional fifths possible in respect to one principal — that if he denies the fifth (i. e. he asserts that he has repaid both capital and fifth, but has not really paid the latter, for which a claim is now made against him) and takes an oath that he has paid it, but afterwards admits the claim, then he must now bring (pay) a fifth in addition to this fifth (a fifth of the original fifth which now has become the קרן in addition to it), and so he keeps on adding a fifth to the original fifth until the principal about which he takes an oath becomes less in value than a P’rutah (Sifra, Vayikra Dibbura d'Chovah, Section 13 12; Bava Kamma 103a).