Kitab At-Tauhid is the book by which Muhammad ibn Abdul-Wahhab is best known and the text most commonly set as a first serious study in Aqidah. Its authority rests on its method: the Shaykh states a principle and then lets the Qur'an and the authentic Sunnah carry the argument. There is very little of the author's own voice in it, and that is deliberate.
What It Establishes
The three categories of monotheism — Lordship, worship, and the Names and Attributes — and then, at much greater length, what breaks them. Major and minor shirk, supplication directed to the dead, amulets and charms, oaths by other than Allah, seeking omens, riya', and excess in venerating the righteous each receive a chapter with the relevant evidences and the words of the early scholars.
The essence of the Qur'an and Sunnah on this subject is placed in a very simple manner, which is what makes the book teachable to a beginner and inexhaustible to a scholar.
Studying It
It is short and dense, and it rewards being taken slowly — ideally with a teacher or with a commentary alongside. Fath Al-Majeed is the classical companion; several modern explanations are also available.
Related Reading
الوصف بالعربية
كتاب التوحيد للإمام محمد بن عبد الوهاب رحمه الله، أشهر كتبه وأكثر ما يُبتدأ به في دراسة العقيدة.
ومنهجه هو مصدر قوّته: يعقد الشيخ الباب ثم يسوق آيات القرآن والأحاديث الصحيحة فتحمل هي الحجة، وليس فيه من كلام المؤلف إلا اليسير، وذلك مقصود.
ويقرّر الكتاب أقسام التوحيد الثلاثة، ثم يطيل في بيان ما ينقضها: الشرك الأكبر والأصغر، ودعاء الأموات، والتمائم والرقى الشركية، والحلف بغير الله، والتطيّر، والرياء، والغلو في الصالحين — كل مسألة في بابها مع أدلتها وأقوال السلف فيها.
وهو كتاب وجيز عميق، يُقرأ متأنيًا، والأولى أن يُدرس على شيخ أو مع شرح معتمد كـ«فتح المجيد».
(1) 
