From Aa'ishah (radiyallaahu 'anhaa) who said that a man sought permission to enter upon the Prophet (salallaahu 'alaihi wa'sallam), so he said:
Give permission to him and what a bad son of his people (or: what a bad man of his people). Then when he entered he spoke politely to him. Aa'ishah said: So I said: O Messenger of Allaah, you said about him what you said and then you spoke politely to him? He said: O Aa'ishah the worst people in station before Allaah on the Day of Resurrection are those whom the people desert, or abandon, in order to save themselves from their evil speech.
[Author's text abridged hereafter]
It will also not be hidden that one of the best ways of cementing ties and improving relations is: