The Gemara in Berachos 12b says "They sought to establish [various passages] in the Shema" and "they establish[ed] the passage of tzitzis in the Shema" (Artscroll trans.)
I had thought that the obligation to recite the Shema was biblical. Who established the passage of tzitzis in the Shema, and if only this passage was established - with Shema and V'haya being biblical requirements - does this make Vayomer derabanan?
Most Rishonim it seems do view the final paragraph of Shema as rabbinic in origin.
Rashba to Brachot 13b understands that only the first verse is a Biblical requirement from the story that Rabbi Yehuda HaNasi used it alone to fulfill his obligation in certain circumstances.
Rashi on Brachot 2a implies that only the first paragraph is a Biblical requirement by stating that one fulfills one's nighttime obligation by reading THE FIRST PARAGRAPH on his bed.
The Yerei'im concurs citing Brachot 16a that workers need only recite the first paragraph.
The Peri Chadash (OC 67) understands Rabbeinu Yonah (Brachot 1a) as understanding that the first two paragraphs are biblical.
The Rambam (Keriat Shema 1:3) when simply read seems to imply that all three paragraphs are a biblical requirement, but the Kesef Mishna understands him to be limiting the biblical requirement to the first verse.
More discussion can be found in the commentaries to Shulchan Aruch OC 67 and in this excellent article.
