The Messenger of Allah ﷺ said, "Shall I inform you of the greatest of major sins?"We said, "Yes, Messenger of Allah."He said, "Associating partners with Allah, and disobedience to parents." He had been reclining, then he sat up and said, "And beware of false speech and false testimony. Beware of false speech and false testimony."He kept repeating it until I thought he would never stop.
قال رسول الله ﷺ: ألا أنبئكم بأكبر الكبائر قلنا: بلى يا رسول الله قال: الإشراك بالله، وعقوق الوالدين وكان متكئا فجلس. فقال: ألا وقول الزور، وشهادة الزور، ألا وقول الزور، وشهادة الزور فما زال يقولها، حتى قلت: لا يسكت.
Bukhari narrated it in Al-Adab (5976), and Muslim in Al-Iman (87), both of them through Saeed Jariri, from Abdul-Rahman bin Abu Bakra, from his father, who mentioned it.