The Prophet ﷺ asked, "Shall I tell you about the greatest of the major sins?" He repeated this three times.They said, "Yes, Messenger of Allah."He said, "Associating partners with Allah, and disobedience to parents." Then he sat up, having been reclining, and said, "And beware of false speech."He kept repeating it until we wished he would stop.
قال النبي ﷺ: ألا أنبئكم بأكبر الكبائر؟ ثلاثا، قالوا: بلى يا رسول الله، قال: الإشراك بالله، وعقوق الوالدين، - وجلس وكان متكئا فقال- ألا وقول الزور قال: فما زال يكررها حتى قلنا: ليته سكت.
Bukhari narrated it in the Book of Testimonies (2654), and Muslim in the Book of Faith (87), both through the route of Saeed Jariri, who said, Abdul-Rahman bin Abu Bakra narrated to us, from Abu Bakra, and he mentioned it.