It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "There is nothing that separates the believing servant from the disbeliever except the prayer, that is, abandoning the prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6496