Sūrah No.109. Revealed in Makkah, 6 verses.
This Sūrah was revealed in the early Makkan period when the Prophet a and the early Muslims were under a lot of pressure to abandon their mission or merge their beliefs with the polytheists. The Prophet a was firm and uncompromising.
This Sūrah has been given extraordinary importance in Hadith due to its strong content. It is recommended to recite this Sūrah before sleeping as it is a disassociation from polytheism. Imam al-Sādiq (a) narrates from his father that after reciting this Sūrah he would say ‘I worship only One God; I worship only One God’.
The Prophet a has said that the best companion to take on a trip who would be of great benefit is the recitation of al-Kāfirūn, al-Nasr, al-Ikhlās, al-Falaq and al-Nās.
The Prophet a has also said: Whoever recites Sūrat al- Kāfirūn is as if he has recited a fourth of the Quran. The rebellious Shayātin distance themselves from him, he will be free of polytheism, and he will be safe from the great fear (on the Day of Judgement).
Note: This reward will be for the one who absorbs the message of the Sūrah and completely disassociates himself from polytheism.
The Sūrah is a response to the polytheists who were demanding that they come together and worship both One God as well as their idols. This proposal was rejected and the Sūrah firmly states that there can be no such compromise.
1) There can be no compromise with the enemies of Islam.
2) The belief in only One God is completely disassociated from polytheistic beliefs.
The entire Sūra.
Check these verses which talk about the futility of belief in other gods: Q 5:76, 16:20, and 34:22.