“The Messenger of Allah ﷺ said: ‘The covenant that distinguishes between us and them is prayer; so whoever leaves it, he has committed Kufr.’” (Using translation from Ibn Mājah 1079)
سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ الْعَهْدُ الَّذِي بَيْنَنَا وَبَيْنَهُمُ الصَّلَاةُ فَمَنْ تَرَكَهَا فَقَدْ كَفَرَ