[Avodah] Rambam Hilchot Qriyat Shema

[Ben Waxman via Avodah]

Rambam Hilchot Qriyat Shema A:4 brings in  the famous midrash about 
Yaacov's sons saying Shema to justify or explain why we say "Baruch Shem 
Kavod . . .". This seemed different, out of place, to me. Why bring in a 
source? Because interjecting these words is so foreign that even a dry 
halacha guide demands that they be sourced?

Does the Rambam bring in a midrash in other places to justify a practice?

Ben