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.