Sahih al-Bukhari, Hadith 7114 ⓘ
Narrated Abi Asha'sha: Hudhaifa said, 'In fact, it was hypocrisy that existed in the lifetime of the Prophet but today it is Kufr (disbelief) after belief.'
حَدَّثَنَا خَلاَّدٌ، حَدَّثَنَا مِسْعَرٌ، عَنْ حَبِيبِ بْنِ أَبِي ثَابِتٍ، عَنْ أَبِي الشَّعْثَاءِ، عَنْ حُذَيْفَةَ، قَالَ إِنَّمَا كَانَ النِّفَاقُ عَلَى عَهْدِ النَّبِيِّ صلى الله عليه وسلم فَأَمَّا الْيَوْمَ فَإِنَّمَا هُوَ الْكُفْرُ بَعْدَ الإِيمَانِ.
also referenced under: Book 92, Hadith 61 (In-Book) & Volume 9, Book 88, Hadith 230 (USC-MSA)