Translation of the verse 53 from Surah Al-Isra’ : Number of verses 111 - - page 287 - Part 15.
And say to My slaves (i.e. the true believers of Islamic Monotheism) that they should (only) say those words that are the best. (Because) Shaitan (Satan) verily, sows disagreements among them. Surely, Shaitan (Satan) is to man a plain enemy.
And tell My servants to say that which is best. Indeed, Satan induces [dissension] among them. Indeed Satan is ever, to mankind, a clear enemy.
(17:53) And O Muhammad!, say to My servants, *57 "They should utter only that which is the best of all. *58 In reality, it is Satan who tries to sow discord between human beings. The fact is that Satan is the avowed enemy of man. *59
*57) "The believers."
*58) 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 inspite of the provoking behaviour of the opponents.
*59) 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. "