:: Say those things that are best ::

Say to My servants that they should (only) say those things that are best: for Satan doth sow dissensions among them: For Satan is to man an avowed enemy.

( سورة الإسراء , Al-Isra, Chapter #17, Verse #53)

According to Tafsir by Sayyid Abul Ala Maududi,

The believers have been enjoined to say only the best things even in their discussion with the disbelievers and other opponents of their Faith. They should neither use harsh words nor make exaggerated statements. They should be cool in their conversation and say only what is true and dignified in spite of the provoking behavior of the opponents.

The believers have been forewarned to guard against the provocations of Satan, as if to say, "While answering your opponents, if you feel that you are being aroused to anger, you should at once understand that it is Satan who is exciting you in order to do harm to your dispute, in which he wants to engage human beings for sowing discord between them."