Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says that one day the Prophet (peace and blessings be upon him) came out to us and said: "None of you should convey to me anything about my Companions, for I love that when I come out to you my heart is free of ill feeling." He says: Some wealth came, and he (peace and blessings be upon him) distributed it. Then I heard two men saying: The one who made this distribution neither sought the pleasure of Allah nor the Home of the Hereafter. I heard and understood what they said, and I came to the Prophet (peace and blessings be upon him) and said: O Messenger of Allah, you had said: "None of you should convey to me anything about my Companions, for I love that when I come out to you my heart is free of ill feeling." I heard so-and-so and so-and-so saying such-and-such. At that, his (peace and blessings be upon him) face turned red with anger, and he said: "Leave us alone; Musa (peace be upon him) was hurt with more than this, yet he was patient."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16675
Al-Hasan (may Allah have mercy on him) says that the Prophet (peace and blessings be upon him) would not recognise lies (accusations), nor would he accept what one person said against another.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16676
Abdur-Rahman bin al-Harith bin Hisham says: I heard a bishop from the people of Najran speaking to Sayyiduna Umar (may Allah be pleased with him), saying: O Commander of the Believers, beware of the killer of three. Sayyiduna Umar (may Allah be pleased with him) said: What is meant by the killer of three? He said: The man who comes to the ruler (imam) with a lie, and the ruler kills the man about whom he spoke; so it is as though he has killed himself, that man, and the ruler.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16677
Sayyiduna Abbas (may Allah be pleased with him) said to his son Abdullah (may Allah be pleased with him): Umar (may Allah be pleased with him) has honoured you greatly, has seated you close to him, and has seated you alongside people whom you are not like. So remember three things from me: never lie, never disclose a secret, and never backbite anyone in his presence.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16678