‘Abdullah bin Buraidah narrated that his father said:“The Messenger of Allah (ﷺ) 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 " .
IbnMaja
Establishing the Prayer and the Sunnah Regarding Them • Hadith 1079