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]