ALLAH 
SAYS: “And avoid uttering falsehoods.” [1].
SAYS: “And avoid uttering falsehoods.” [1].
Allah also says: “And do not pursue that of which you have no knowledge. Verily the hearing, sight and heart will all be questioned about.” [2].
also says: “And do not pursue that of which you have no knowledge. Verily the hearing, sight and heart will all be questioned about.” [2].
We relate in the Ṣaḥīḥs of al-Bukhārī and Muslim that Abū Bakrah Nufay‘ ibn al-Ḥārith 
reported: “The Messenger of Allah 
said thrice: ‘Should I not inform you of the greatest of the major sins?’ We replied: ‘Yes, Messenger of Allah.’ He said: ‘Associating partners with Allah, and disobeying one’s parents.’ He had been reclining, but sat up and said: ‘Beware of false speech and false witness.’ He continued to repeat it until we said: ‘Alas! If only he would stop!’” [3].
reported: “The Messenger of Allah said thrice: ‘Should I not inform you of the greatest of the major sins?’ We replied: ‘Yes, Messenger of Allah.’ He said: ‘Associating partners with Allah, and disobeying one’s parents.’ He had been reclining, but sat up and said: ‘Beware of false speech and false witness.’ He continued to repeat it until we said: ‘Alas! If only he would stop!’” [3].I say that there are many hadiths on this subject, but what I have cited is sufficient and there is consensus about it.
References
[1] Qur’ān 22:30.
[2] Qur’ān 17:36.
[3] Al-Bukhārī (2654) and Muslim (87).