Sunan Ibn Majah, Book 5, Hadith 1132 (In-Book) ⓘ
‘Abdullah bin Buraidah narrated that his father said: “The Messenger of Allah said: ‘The covenant that distinguishes between us and them is prayer; so whoever leaves it, he has committed Kufr.’”
حَدَّثَنَا إِسْمَاعِيلُ بْنُ إِبْرَاهِيمَ الْبَالِسِيُّ، حَدَّثَنَا عَلِيُّ بْنُ الْحَسَنِ بْنِ شَقِيقٍ، حَدَّثَنَا حُسَيْنُ بْنُ وَاقِدٍ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ بُرَيْدَةَ، عَنْ أَبِيهِ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " الْعَهْدُ الَّذِي بَيْنَنَا وَبَيْنَهُمُ الصَّلاَةُ فَمَنْ تَرَكَهَا فَقَدْ كَفَرَ " .
also referenced under: Hadith 1079 (Reference) & Volume 2, Book 5, Hadith 1079 (DarusSalam)