Ruling on flattering a liar
11-8-2013 | IslamWeb
Question:
Is 'mujameleh' allowed in Islam? I mean to say nice words to a liar ("What you say is correct", "You are a truthful person", etc.) to try to persuade him to give you your rights, or to give compliments to someone to make him like you while you do not mean any of those words? I see it everywhere around me but I honestly can't stand it. To me, it seems like being 'two-faced' and the Prophet (PBUH) has warned against that. But maybe I am not correct? Please explain in detail all about this phenomenon. May Allah bless you.
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad 
is His slave and Messenger.
A Muslim should not flatter someone for an evil deed that he had done and not deny it as a way of earning that person’s love or compassion; so one should not say to someone who told a lie that he is truthful or that he is right as this is a lie and it is flattering for a lie.
Shaykh ‘Abdul ‘Azeez ibn Muhammad ibn ‘Abdul Muhsin As-Salmaan 
said: “What some people do like flattering each other in listening to evil and watching evil, and listening to backbiting and slandering and the like, then this is a very dispraised cowardliness and who does that is sinful if he does not deny it or leave the people who do it.”
But a person may keep quiet on some kind of evil in order to wait for the appropriate moment to deny it, and in this case, he is praised in what he does because sometimes hastening to deny it may lead to a greater evil.
As for flattering others for what is not evil, like gentleness in dealing with them and pretending to show one’s kindness and love to them, then this is permissible. Al-Ghazaali said: “Flattery, whether it is pretended or it is one’s nature, diminishes the flame of enmity on both sides and decreases the desire for it, and it accustoms the hearts to love each other and have compassion for each other.”
For more benefit about the meaning of double-faced and dispraising the double-faced, please refer to Fatwa 85882.
Allaah Knows best.