The Messenger of Allah ﷺ said, "The covenant between us and them is the prayer, so whoever abandons it has committed disbelief."
أخبرنا الحسين بن حريث قال أنبأنا الفضل بن موسى عن الحسين بن واقد
قال رسول الله ﷺ إن العهد الذي بيننا وبينهم الصلاة فمن تركها فقد كفر
Its isnad is sahih. Reported by Tirmidhi, in the Book of Faith, chapter on what has been said about abandoning prayer, hadith 2621, from Husayn bin Hurayth with this chain, and he said, hasan sahih gharib. It is also in Al-Kubra, hadith 329, and Sunan Ibn Majah, hadith 1079, from the hadith of Ibn Waqid.