Here you can find ebooks and articles about the meaning of La ilaha illa Allah, and what it contains of issues such as: Al-Kufr bit-Taghut, declaring takfir upon the mushrikun, the pillars and conditions of Tawhid and more.
For a summarized overview of important issues on Tawhid refer to the book “An introduction to Tawhid and Sunnah”.
UPDATED!! Some issues regarding takfir
Mufid Al-Mustafid fi Kufr Tarik At-Tawhid – by Muhammad ibn Abdul-Wahhab
The Six Principles – by Muhammad ibn Abdul-Wahhab
The Four Principles – by Muhammad ibn Abdul-Wahhab
Explanation of six places in the Sirah – by Muhammad ibn Abdul-Wahhab
Takfir upon the mushrikun and its relation to Kufr bit-Taghut – by Ahmad ibn ‘Umar Al-Hazimi
The mistaken mujtahid in Tawhid is kafir
The shafa’ah (intercession) according to the Quran and Sunnah
Examples of shirk and kufr today
When does obeying someone in sinning amount to major shirk?
What did the people of the Messengers understand from the da’wah towards Lā ilāha illa Allāh?