Good Manners and Form (Al-Adab)
Ṣaḥīḥ al-Bukhārī 6054
أَىْ عَائِشَةُ، إِنَّ شَرَّ النَّاسِ مَنْ تَرَكَهُ النَّاسُ ـ أَوْ وَدَعَهُ النَّاسُ ـ اتِّقَاءَ فُحْشِهِ
ay ʿāʾishah, inna sharra an-nāsi man tarakah an-nāsu aw wadaʿah an-nāsu āttiqāʾa fuḥshihi
Transliteration generated from the Arabic vowel marks
The full narration
Narrated `Aisha:A man asked permission to enter upon Allah's Messenger (ﷺ). The Prophet (ﷺ) said, "Admit him. What an evil brother of his people or a son of his people." But when the man entered, the Prophet (ﷺ) spoke to him in a very polite manner. (And when that person left) I said, "O Allah's Messenger (ﷺ)! You had said what you had said, yet you spoke to him in a very polite manner?" The Prophet (ﷺ) said, "O `Aisha! The worst people are those whom the people desert or leave in order to save themselves from their dirty language or from their transgression
Source
Ṣaḥīḥ al-Bukhārī · 6054