Do not select bad names

It is not permissible to mention any Muslim with a bad name, though; he is a sinner as it is mentioned in the Glorious Quran:

وَ لَا تَلۡمِزُوۡۤا اَنۡفُسَکُمۡ وَ لَا تَنَابَزُوۡا بِالۡاَلۡقَابِ ؕ
 بِئۡسَ الِاسۡمُ الۡفُسُوۡقُ بَعۡدَ الۡاِیۡمَانِ ۚ وَ مَنۡ لَّمۡ یَتُبۡ فَاُولٰٓئِکَ ہُمُ الظّٰلِمُوۡنَ ﴿۱۱﴾

Translation from Kanz-ul-Iman: ‘And do not insult one another, nor assign evil nicknames; how base it is to be called a sinner after being a Muslim! And whoever does not repent - then it is they who are unjust.’

(Part 26, Surah Al-Hujurat, verse 11)

It is stated in Tafseer (commentary) of Khaza’in-ul-Irfan: Do not give bad names to one another which are disapproving for them. Ruling: Sayyiduna Ibn-e-Abbas رَضِیَ الـلّٰـهُ تَعَالٰی عَـنْهُمَا said: If any person has sought forgiveness from any wrongdoing, after that, it is prohibited to make him feel ashamed of his that evil act and it is also prohibited. Some blessed scholars have said: To call any Muslim dog, donkey or pig also falls in the same category. Some blessed scholars said: It refers to those titles which defame or disrespect Muslim and those are disapproving for him but words of praising which are true are not prohibited such as the title of Sayyiduna Abu Bakr رَضِىَ اللهُ تَعَالٰی عَـنْهُ is ‘Ateeq’, the title of Sayyiduna Umar  رَضِىَ اللهُ تَعَالٰی عَـنْهُ is ‘Farooq’, title of Sayyiduna Usman رَضِىَ اللهُ تَعَالٰی عَـنْهُ is ‘Ghani’, the title of Sayyiduna Ali رَضِىَ اللهُ تَعَالٰی عَـنْهُ is ‘Abu Turab’ and the title of Sayyiduna Khalid رَضِىَ اللهُ تَعَالٰی عَـنْهُ is ‘Saifullah’ and those titles which become one’s recognition and are not disapproving for him are also not prohibited for example اعمش، اعرج.

Keep yourself attached to the people of knowledge and ask them whatever you do not know as it is mentioned in the Glorious Quran: