'Abdullah ibne-'Amr Radiyallahu 'anhuma narrates that Rasulullah Sallallahu 'alaihi wasallam was asked: Who is the most excellent amongst people? He replied: Everyone whose heart is Makhmum and tongue is truthful. The Sahabah asked: We understand whose tongue is truthful, but what does a Makhmum heart mean? He replied: The one who is a Muttaqi (fearful of Allah) is pure of heart, free of sins and without injustice, hatred or jealousy for any one. (Ibne-Majah)

Hazrat Jabir Bin Abdullah and Hazrat Talha Bin Sahl Ansari [RA] narrates that Prophet Muhammad PBUH said: The person who quits support to his brother at that moment when his honor is being attacked and damaged, Allah shall deprive him of His blessings when he shall be wishing for Allah’s help. And the person who provides help when the other’s honor is attacked and damaged, Allah shall provide help at the time when he shall be  wishing for Allah’s help[. [Abu Dawud]

“O you who have embraced Islam with your tongues but in whose hearts faith has not yet entered, do not disparage Muslims and do not seek their defects.  Verily, God will seek out the defects of he who is after their defects; and one who has God after his defects will be humiliated, even in his own abode.” [Abu Dawud]

The Prophet (s) said to Hazrat Muaz (R.A), "Shall I not tell you how to control all that?" I said, "Yes do, O Messenger of Allah." So he held his tongue between his fingers, and then he said: "Restrain this." I said, "Oh Prophet of Allah, are we accountable for what we say?" He (s) said, "people will be thrown face down into Hell only on account of the harvest of their tongue”