These are nice benefits from a compilation of Shaykh al-Uthaymīn's explanation of Kitāb al-Tawḥīd.
The categories of Tawḥīd are three:
- Tawḥīd al-Rubūbiyyah: It is to single out Allāh with (actions of) creation ( khalq), the dominion (al-mulk), and regulation of affairs (al-tadbīr).
- Tawḥīd al-Ulūhiyyah: It is to single out Allāh with all worship.
- Tawḥīd al-Asmāʾ wa-al-Ṣifāt: It is to single out Allāh with His Names and His Attributes without any taḥrīf(distortion), taʿtīl (negating or denying), takyeef (seeking after the specific details of Allāh's Attributes), nor tamthīl (likening Allāh or one of His Attributes to His Creation).
Tawḥīd cannot be established without two matters:2
- al-Nafī (Negation).
- al-Ithbāt (Affirmation).
 Source: Abū Mu hammad Ismāʿīl ibn Marshūd ibn Ibrāhīm al-Ramīh, al-Fawāʿid al-Muntaqāh min Sharḥ Kitāb al-Tawḥīd by Shaykh al-ʿUthaymīn.
 TN: Shaykh ibn al-ʿUthaymīn said: "Linguistically, Tawḥīd is the noun derived from the Arabic root verb: وَحَّدَ/يُوَحِّد (waḥḥada/yuwaḥiddu) which means to make something into one. This is not accomplished except by a negation and affirmation, both together - negating this characteristic from anything other than the thing which is being singled out, and affirming it to that thing.
For example, we say that mankind will not fulfill the concept of Tawḥīd unless and until they testify that nothing deserves any form of worship except Allāh. By this, we negate any right of worship to anyone or anything other than Allāh (subḥānaḥu wa taʿāla), and we affirm it to Allāh alone. This is because negation alone equates to an absolute and complete negation, just as affirmation alone does not restrict others from sharing in that characteristic.
So if you were to say, "So and so is standing," then you have affirmed that he is indeed standing but you have not singled him out alone, restricting this action only to him because it is possible, based on this saying alone, that someone else could also be standing with him. Similarly, if you were to say, "No one is standing," then you have absolutely and completely negated the action of standing for anyone. However, if you said, "No one is standing except Zayd," then you have singled out Zayd alone with the action of standing, negating it from anyone other than him. This is the true actualization of Tawḥīd in reality - meaning that Tawḥīd is not fulfilled unless it contains both negation and affirmation." [Tawḥīd, Its Meaning & Categories, Shaykh Muḥammad ibn Ṣāliḥ al-ʿUthaymīn.
Translated by Abū al-Zubayr Harrison].