Almighty Allah says about mischief in the Holy Qur’an:1
‘And seek, in that which Allah has given thee, the Home of the Hereafter; and neglect not thy lot in this world; and do good to others as Allah has done good to thee; and seek not to make mischief in the earth, verily Allah loves not those who make mischief.’
Hazrat Mu‘adh Bin Jabal(ra) relates that the Holy Prophet(sa) said, ‘Combat is of two types: One that is waged for the pleasure of Allah under the leadership of an Imam [divinely guided leader]. A person engaged in such combat spends his best property in the way of Allah, is comforting his companions, and avoids mischief. For such a person, everything — his sleeping and waking time — earns merit in the sight of Allah. And there is another who engages in combat for pride, ostentation, and to talk about his valour. He disobeys the Imam and creates mischief in the earth. Such a one can never equal the first one in rank.’ (Sunano Abi Dawud, Kitab-ul-Jihad, Babu fi man yaghzu wa yaltamis-ud-Dunya)
Hazrat Asma’ Bint Yazid(ra) narrates that the Holy Prophet(sa) said, ‘Should I inform you about the best of people?’ The Companions(ra) said, ‘Certainly, tell us O Prophet of Allah.’ He said, ‘When they witness a desirable scene, they start remembering Allah.’ Then he said, ‘Should I tell you about the worst of people? The worst people are those who go about backbiting and creating discord between people. Their wish is that the obedient servants of Allah get involved in sin.’ (Musnadu Ahmadabni Hanbal, vol. 6, p. 459, printed in Beirut)
The Promised Messiah(as) says:
Do not engage in fighting or discord with those who leave you because you have joined a Movement established by Almighty Allah; instead, pray for them in secret that Almighty Allah may grant them the insight and cognition that He has granted you. With your pious example and good behaviour, prove that you have adopted the right path. Listen! I am appointed to admonish you repeatedly to avoid all occasions of discord and disturbance. Have patience even if you hear abuse. Respond to evil with goodness. If you encounter discord, slip away from that situation or respond with kind words…. I do not like when I learn that someone has quarrelled despite being a member of my Jama‘at. Almighty Allah does not like that the jama‘at that is destined to become a model for mankind should adopt such ways, which are not the ways of righteousness. Indeed, I tell you that Almighty Allah has emphasised this matter so much that if someone — declaring his membership of the Jama‘at — does not show patience and perseverance, he does not belong to this Jama‘at. The utmost cause of your provocation might be that you hear people abusing me. Leave that matter for God to decide. You cannot judge it. Leave my affair to God; you should show patience even in the face of such abuse. (Malfuzat, new edition, vol. 4, p. 157)
1 al-Qasas, 28:78