Sunan Ibn Majah
1079
Sahih+3

‘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.’”

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi