In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Allaah’s Messenger [peace and blessings of Allaah be upon him] said, “Verily, the worst act of usury is to attack the honour of a Muslim without a just cause”. (1)
“Verily, the worst act of usury is to attack the honour of a Muslim”– Meaning, the greater in evil and the more severely prohibited is to unleash the tongue against the honour of a Muslim by belittling him, behaving arrogantly towards him and speaking ill against him by way of slander or verbal abuse. This becomes more severe in prohibition because honour is more noble than one’s self and wealth.
“Without a just cause”-Meaning, this shows that there are cases in which one is allowed to speak about someone, saying, “Such and such is an oppressor or transgressor”, or making a mention of an innovator and an open sinner with the intention to issue warning. (2)
This (i.e. violating the honour of a Muslim) has been referred to as usury because the transgressor establishes his honour and then goes beyond it, so it is as if he has added an increase that encroaches the boundaries in relation to the honour of a Muslim which is more valuable than his wealth. At-Teebee [may Allaah have mercy upon him,] said, “Honour is included in the types of wealth from the angle of emphasis, usury is categorized into one that is customary and it is what is taken as an addition from debtors, and that which is not customary such as a person attacking the honour of someone with his tongue. Al-Qaadhee [may Allaah have mercy upon him] said, ‘Attacking a Muslim’s honour is to deal with him more than what he deserves of that which is to be said about him, or more than what is allowed to say about him, and this is why it is likened to usury and considered one of its types. Then it is considered worse because it contains more harm and severer in corruption'”. (3)
Shaikhul Islaam Ibn Taymiyyah [may Allaah have mercy upon him] said, “Lying against an individual is absolutely forbidden- whether the man (i.e. the one lied against) is a Muslim or a disbeliever, righteous or a wicked sinner; but fabricating lies against a believer is more severe. (4)
[Ref 1: Abu Daawud 4876]
[Ref 2: An Excerpt from ‘Awnul Mabood Sharh Sunan Abee Daawud’ 13/152. Slightly paraphrased]
[Ref 3: An Excerpt from ‘Mirqaatul Mafaateeh Sharh Mishkaat Al-Masaabeeh’ 8/3157. Slightly paraphrased]
[Ref 4: Majmoo Al-Fataawaa 28/223]