Abu Al-‘Aliyah (may Allah have mercy on him) narrates that a man recited this verse before him: «يَوْمَيَأْتِيبَعْضُآيَاتِرَبِّكَلَايَنْفَعُنَفْسٌإِيمَانُهَا» So he did not object to his recitation, because he would not object to anyone’s recitation. Then Abu Al-‘Aliyah himself recited the verse as follows: ﴿يَوْمَيَأْتِيبَعْضُآيَاتِرَبِّكَلَايَنْفَعُنَفْسًاإِيمَانُهَالَمْتَكُنْآمَنَتْمِنْقَبْلُ﴾. The narrator says: I mentioned this to Ibrahim Al-Nakha‘i (may Allah have mercy on him), so he said: I think your companion must have heard, or it has reached him, that whoever denies even a single letter of the Qur’an, it is as if he has denied the entire Qur’an.
Hadith Referenceسنن سعید بن منصور / كتاب التفسير / 936