Heidegger's Bible Handbook: Ruth: Authorship

2. The author of this appears to be the same as of the Book of Judges.

That the author of this book is Samuel, the Jews approve: but others contend that this was extracted from that great book of the Annals of the Kings of Judah and Israel, of which repeated mention is made in the books of Kings. We think that concerning the Author of this book a similar judgment is to be made to that which we set forth concerning the author of the Book of Judges, of which this is an appendix, especially since it is evident from Ruth 4:21, 22, it was written in the order in which we now have it not before the times of David.