Mu'jam Kabir Tabarani 8492 — The most truthful word is the Book

Sayyiduna Abdullah (may Allah be pleased with him) said: "The most truthful word is the Book of Allah, the best guidance is the guidance of Muhammad (peace and blessings be upon him), and the worst of things are newly invented matters. What you are promised is surely coming, and you cannot frustrate (Allah). Indeed, the far is that which is not coming. Beware! Hold fast to truthfulness, for it leads to Paradise. A man keeps speaking the truth until he is written with Allah as a siddiq (truthful one), righteousness becomes firmly established in his heart, and wickedness does not find in his heart even the space of a needle in which to settle. Beware! Keep away from lying, for it leads to Hell. A man keeps lying until he is written with Allah as a great liar, and wickedness settles in his heart, so that there does not remain in his heart even the space of a needle in which (righteousness) could settle."