Bearing false witness is absolutely Haram (prohibited). Allah (Exalted be He) states:
So shun the abomination (worshipping) of idol, and shun lying speech (false statements)
It was authentically reported on the authority of
Abu Bakrah (may Allah be pleased with him) that the Prophet (peace be upon him) stated:
Should I inform you about the gravest major sins? We said: Yes, O Allah's Messenger! He said: To associate others in worship with Allah and to be undutiful to one's parents. The Prophet (peace be upon him) then sat up after he had been reclining (on a pillow) and said: And I warn you against giving a false testimony, and he kept on repeating that warning till we wished he would stop saying it.
Reported by Al-Bukhari and Muslim in the Two Sahih (authentic) Books of Hadith.
(Part No. 23; Page No. 510) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.