Al-Ikhtiyar li Ta'lil al-Mukhtar - Imam al-Mawsili (683H)

This is a book of Hanafi jurisprudence. Even more, it's a major one, it's an authority among the Ahnaf for centuries.

The author has compiled earlier in his youth an abridged book in Hanafi jurisprudence which he titled “al-Mukhtar lil Fatwa”. This book is studied and many works in the Hanafi Madhhab were made from it. Some scholars who studied his book asked him to provide an exposition indicating the causes of his legal issues and their meanings and mention additional branches (for more explanation). They also asked him to report any disagreement among the followers of the Hanafi School and explain its cause.

So he put forward this exposition, which he called “al Ikhtiyaar li Ta’leel al-Mukhtaar. It began with the book of purity and ended with the book of inheritance.