´‘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.’”
Hadith Referenceسنن ابن ماجه / كتاب إقامة الصلاة والسنة / 1079
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:إسناده صحيح
´Narrated Abdullah bin Buraidah narrated from his father:` that the Messenger of Allah (ﷺ) said: "The covenant between us and them is the Salat, so whoever abandons it he has committed disbelief."
Shaykh Dr. Abdur Rahman Freywai
Explanation: 1: That is, as long as they continue to perform the prayer (salah), we will apply the rulings of Islam upon them, and when they abandon the prayer, then the rulings for disbelievers will be applied to them, because the covenant between us and them is the prayer, and when the prayer is abandoned, it is as if the covenant has ended.
Source: Sunan al-Tirmidhi – Majlis ‘Ilmi Dar al-Da‘wah, New Delhi Edition, Page: 2621