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Surah 2. Al-Baqara
Ayah 161 - 162
161إِنَّ ٱلَّذِينَ كَفَرُوا۟ وَمَاتُوا۟ وَهُمْ كُفَّارٌ أُو۟لَـٰٓئِكَ عَلَيْهِمْ لَعْنَةُ ٱللَّهِ وَٱلْمَلَـٰٓئِكَةِ وَٱلنَّاسِ أَجْمَعِينَ
162خَـٰلِدِينَ فِيهَا ۖ لَا يُخَفَّفُ عَنْهُمُ ٱلْعَذَابُ وَلَا هُمْ يُنظَرُونَ
[161-162] Those who adopted the way of disbelief161 and died as disbelievers, are accursed of Allah and of angels and of all mankind: they shall remain accursed for ever. Their punishment shall not be lightened, nor shall they be reprieved.
161The literal meaning of the word kufr is "to conceal". By and by it came to be used for the concealment of the Truth and then for its rejection, as the antonym of imam n. Iman means to believe, to accept and to admit, and kufr means to disbelieve, to reject and to oppose. According to the Qur'an, one shall be guilty of kufr.
(1) If one does not believe in Allah at all or refuses to accept Him as the Supreme Authority or as one's Master and that of the entire Universe or as the only God of worship, or
(2) If one professes to acknowledge Allah but refuses to accept His commandments and Guidance as the sole source of the knowledge of Truth and of Law, or
(3) If one accepts on principle the Guidance of Allah, but refuses to accept the authority of the Messengers whom Allah has sent with His Commandments and Guidance, or
4) If one accepts a particular Messenger (or Messengers) and rejects others according to one's whim or prejudices, or
(5) If one discards the whole or any part of the Islamic creed, or its code of life, or the teachings of the Messenger, or
(6) If one accepts all these things in theory but discards the Commandments of God deliberately in practice and persists in this conduct and leads a life of rebellion instead of submission.
All the above modes of thought and action are rebellion against Allah and are kufr according to the Qur'an. Besides the above usages, the Qur'an sometimes uses the word kufr in the sense of ingratitude as an antonym of shukr. Shukr means that one should be grateful only to Him Who has bestowed the blessing, should appreciate His favour,.should use and spend the blessing only according to His Will, and should submit to Him completely and faithfully like a loyal servant. On the contrary, kufr or ingratitude is that one should either refuse to acknowledge the favour of one's benefactor, and should regard it as a result of one's own ability, or as a favour and result of the influence of another one, or should depreciate the blessing bestowed by Him and waste it, or should use the blessing against His Will, or should adopt an attitude of rebellion against him inspite of His favours and blessings. Such an attitude of kufr is generally described as ingratitude, disloyalty, rebellion and treason.