I did some quick research and it seems the book you're looking for is called
Al-wajiz fi fiqh al-imam al-shafi'i - The condensed in Imam Shafi'i's Jurisprudence.
As the name indicates, it's a book that contains rulings and opinions of Shafi'i fiqh.
I tried looking for an English translation online, but all I could find were versions in Arabic (
Volume 1 and
Volume 2).
I also thought there might be something in one of his books called
Nasihat al-muluk - Counsel for Kings (available in English
here), but a quick scan didn't reveal any details on what you had mentioned. Feel free to look closer.