Musnad Ahmad 1017:73

Zayd ibn al-Hubab narrated to us, Husayn ibn Waqid narrated to us, Abdullah ibn Buraydah narrated to us, from his father, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Between us and them is the abandonment of prayer; so whoever abandons it has committed disbelief."