Allah سبحانه وتعالى says in the Holy Qur’an,
وَقُلْ لِعِبَادِي يَقُولُوا الَّتِي هِيَ أَحْسَنُ إِنَّ الشَّيْطَانَ يَنزَغُ بَيْنَهُمْ
Shaytaan creates enmity and hatred between us by exploiting what we say to each other. It is human nature to feel hurt by what another says, however shaytaan turns this into hatred. Therefore we should cut this at its root by being extremely careful about what we say to our husband, wife, children, parents, and friends. Rather than speaking harshly, we should train ourselves to speak with love and respect otherwise shaytaan will create divisions between us.
[This short excerpt is based on a brothers' majlis (gathering held for spiritual training) held by Shaykh Abu Yusuf Riyadh ul Haq on 27th February 2002].