'Anas-ibn-Mlaik narrates from the Messenger of Allah [s] who said: "Accept six things from me, then I will accept (and guarantee) the entrance of Heaven for you:
Khisal-i-Saduq, p. 321
Imam Abi-Muhammad-al-'Askari, the eleventh Imam, [a] said: "Wickedness was put inside a house, and the key (of its door) was rendered to be lies."
Bihar-ul-Anwar, vol. 72, p. 263
Imam Sajjad [a] said: "Avoid telling lies irrespective of small or great, whether it is in earnest or joking, because when a person tells a lie in small (things), he dares to tell a lie in great things, too."
Tuhaful-Uqul, p. 201
Once Imam Amir-ul-Mu'mineen Ali [a] was asked about the distance between the truth and untruth and, while he [a] was showing the distance between his eye and ear with his four fingers in order to illustrate this distance as his answer, he said: "What your eyes see is 'truth' and what your ears hear is for the most part 'untruth'."
Bihar-ul-Anwar, vol. 75, p. 196
Imam Baqir [a] said: "Verily, Allah, the exalted, has put some locks on vices, the key of which He has put in wine, but the vice of lying is worse than wine."
AI-Kafi, vol. 2, p. 339
Imam Rida [a] said: "Be truthful and avoid telling lies."
Bihar-ul-Anwar, vol. 78, p. 347