Al-Muzanni reported: Al-Shafi’i, may Allah have mercy on him, said, “Whoever admonishes his brother in private has been sincere to him and protected his reputation. Whoever admonishes him in public has humiliated him and betrayed him.”
Source: Ḥilyat al-Awliyā’ 13854
عن المزني قال الشافعي رحمه الله مَنْ وَعَظَ أَخَاهُ سِرًّا فَقَدْ نَصَحَهُ وَزَانَهُ وَمَنْ وَعَظَهُ عَلانِيَةً فَقَدْ فَضَحَهُ وَخَانَهُ
13854 حلية الأولياء لأبي نعيم الإمام الشافعي