Musnad Ahmad 26:558

Waki’ and Abu Mu’awiyah narrated to us, they said: Al-A’mash narrated to us, from Abu Wa’il, from Abdullah, who said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Beware of lying, for lying leads to wickedness, and wickedness leads to the Fire. And a man continues to lie until he is recorded with Allah as a liar." And he said: The Prophet, may Allah bless him and grant him peace, said: "You must be truthful, for truthfulness leads to righteousness, and righteousness leads to Paradise. And a man—meaning the man—continues to be truthful and strives for truthfulness until he is recorded with Allah as a truthful one (Siddiq)." Abu Mu’awiyah said: "And a man continues to be truthful and strives for truthfulness."