It is reported that Abū Bakr Al-Ṣiddīq – Allāh be pleased with him – said:
Beware of lying, for lying is far removed from īmān.
Abū Bakr Al-Ḵallāl, Al-Sunnah no. 1467, 1470; Al-Bayhaqī, Shuʿab Al-Īmān no. 4463.
Ibn Al-Qayyim said in Al-Fawāʾid,
…Thus, every good action – both outer and inner – comes from truthfulness, and every evil corrupt action – both outer and inner – comes from falsehood and lying.