From Abee Hurayrah (radiyAllaahu ‘anhu) that the Messenger of Allaah (salallaahu ‘alaihi wa sallam) said,

“Whoever calls to guidance has a reward like the example of the reward of those who follow him, not decreasing their reward in any way. And whoever calls to misguidance has upon him the sin like the example of the sin of those who follow him, not decreasing their sin in anyway.”

Narrated by Muslim, no. 2674.

From Abdullah ibn Mas’ood (radhi allaahu anhu) who said that the Messenger of Allah (sallallaahu alayhi wa sallam) said:

I order you to be truthful for verily truthfulness leads to righteousness (al birr) and verily righteousness leads to Paradise. And a man continues to be truthful and strives for truthfulness until he is written as a truthful person with Allah. Beware of Falsehood, for verily falsehood leads to sinning (al-fujoor) and verily sinning leads to the Fire. And a man continues to tell lies and strives upon falsehood until he is written as a liar with Allah. 

[Reported by al-Bukharee (6094) Muslim (105), Ahmed (1/8), Abu Dawood (4989), Malik (16 2/989) at-Tirmidhee (1971 4/347), Ibn Majah (46 1/18), ad- Daarimi (2718 2/210) and the wording is that of Muslim] 

Sufyaan Ibn ‘Abdillaah said: “O Messenger of Allaah, tell me something about Islaam of which I will not ask anyone else besides you (after that).” He sallallaahu alayhi wa sallam said: “Say: ‘I believe in Allaah’ and then be steadfast (upon that).” [Saheeh Muslim, no. 38]

قل ما شئت َ في مسبّة عرضي********** فسكوتي عن اللئيم جواب
ما أنا عادم الجواب و لكن********** ما من الأسد أن تجيب الكلاب

Say what you will in defamation of my honor,
For my silence to the lowly one is an answer.
It is not that I am at a loss for a reply, however,
it is not for the lion to respond to dogs.

From the Dīwān of al-Shafi’ī