Al-Dhahabi reported: Ibn al-Mubarak, may Allah have mercy on him, said, “It is a duty upon the wise man not to belittle three persons: the scholars, the authorities, and his brothers. Indeed, whoever belittles the scholars will lose his place in the Hereafter. Whoever belittles the authorities will lose his place in the world. Whoever belittles his brothers will lose his manhood.”
Source: Siyar A’lām al-Nubalā’ 17/251
عن الذهبي عَنِ ابْنِ الْمُبَارَكِ رحمه الله قَالَ حَقٌّ عَلَى الْعَاقِلِ أَنْ لَا يَسْتَخِفَّ بِثَلَاثَةٍ الْعُلَمَاءِ وَالسَّلَاطِينِ وَالْإِخْوَانِ فَإِنَّهُ مَنِ اسْتَخَفَّ بِالْعُلَمَاءِ ذَهَبَتْ آخِرَتُهُ وَمَنِ اسْتَخَفَّ بِالسُّلْطَانِ ذَهَبَتْ دُنْيَاهُ وَمَنِ اسْتَخَفَّ بِالْإِخْوَانِ ذَهَبَتْ مُرُوءَتُهُ
17/251 سير أعلام النبلاء