Some siddurim have the following phrase in between "ושמו אחד" and "ישתבח":
ובתורתך כתוב לאמר שמע ישראל ה׳ אלקינו ה׳ אחד
"And in Your Torah it is written to say Shema Yisrael Hashem Elokeinu Hashem Echad"
What is the origin of this phrase's insertion, and what is the purpose of its insertion at this point?