Answered by Shaykh Abdurrahman ibn Yusuf Mangera
Should we read Fiqh as Sunnah by Sayyid Sabiq and other books written on Islam by these sorts of people? And should we also read books on other religions.
In the name of Allah he Inspirer of truth.
This work is to be avoided since it encourages one to not adhere to any one of the four traditional schools which the overwhelming majority of Muslims have followed for over thirteen hundred years. Many of the juridical rulings and ijtihad propounded therein by the author contradict the opinions of the four madhahib. Sometimes opinions that do not conform to any one of the four traditional schools are presented as the preferred or superior opinion.
Hence, the choice is now to whether follow one of the four acclaimed traditional schools that have stood the test of history or to follow the ijtihad of someone who came much after the best of generations (khayr al-qurun).
The Messenger of Allah (upon him be peace) said “The best of you is my generation, then those who follow them, then those who follow them (Bukhari, Muslim).
And Allah knows best.
Abdurrahman in Yusuf