Allaah (The Most High) said:
وَقُل لِّعِبَادِي يَقُولُوا الَّتِي هِيَ أَحْسَنُ ۚ إِنَّ الشَّيْطَانَ يَنزَغُ بَيْنَهُمْ ۚ إِنَّ الشَّيْطَانَ كَانَ لِلْإِنسَانِ عَدُوًّا مُّبِينًا
And say to My slaves 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.
Imaam Ibn Katheer (rahimahullaah) stated:
Allaah [The Blessed and Most High] command His slave and Messenger [i.e. Muhammad (sallal-laahu-alayhi-wasallam)] to command Allaah’s believing slaves that they speak to one another in their conversations and discussions with what is better and good, for if they do not do that, shaytaan will sow a state of conflict between them and speech will lead to actions, and thus evil, (blameworthy) argumentation and fighting will arise; for indeed shaytaan is an enemy of Aadam and his children since (the time) he refused to prostrate to Aadam. His enmity is clear and manifest, so because of this, it prohibited for a man to point at his Muslim brother with an iron (instrument), for indeed shaytaan (can entice an evil action) in his hand and he may cause him to strike him (i.e. his Muslim brother) with it.
[Source: Al-Misbaah Al-Muneer Fee Tahdheb Tafseer Ibn katheer’ Surah Al-Israa 17: 53]