Abu Bakrah (May Allah be pleased with him) reported:
The Messenger of Allah ﷺ said, "Shall I not inform you of one of the gravest of the cardinal sins?" We said: "Yes, O Messenger of Allah!" He ﷺ said, "To join others as partners with Allah in worship and to be undutiful to one's parents." The Messenger of Allah ﷺ sat up from his reclining position (in order to stress the importance of what he was going to say) and added, "I warn you making a false statement and giving a false testimony. I warn you against making a false statement and giving a false testimony." The Messenger of Allah ﷺ kept on repeating this (warning) till we wished he should stop.

[Al-Bukhari and Muslim]

وعن أبي بكر رضي الله عنه قال: 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!" فما زال يكررها حتى قلنا: ليته سكت.