It is reported that ʿAbdullāh b. Masʿūd - Allāh be pleased with him - said:

Verily a man continues to be truthful until he is written with Allāh as a true believer (ṣiddīq); and he persists in truthfulness until there is not even the space of a needle for sinfulness left in his heart to settle. And a man lies and persists in lying until there is not even the space of a needle for goodness in his heart to settle.

Wakīʿ b. Al-Jarrāḥ, Al-Zuhd ḥadīth 398.