Muhanna reported: I asked Abu Abdullah Imam Ahmad, may Allah have mercy on him, about enjoining good and forbidding evil, “How should one enjoin it?” Ahmad said, “One should enjoin good with gentleness and humility. If they make him hear what he dislikes, he should not get angry such that he wants to avenge himself.”
Source: al-Amr bil-Maʻrūf lil-Khallāl 1/28
عن مُهَنَّا قَالَ سَأَلْتُ أَبَا عَبْدِ اللَّهِ يعني الإمام أحمد رحمه الله عَنِ الْأَمْرِ بِالْمَعْرُوفِ وَالنَّهْي عَنِ الْمُنْكَرِ كَيْفَ يَنْبَغِي أَنْ يُؤْمَرَ قَالَ يَأْمُرُ بِالرِّفْقِ وَالْخُضُوعِ إِنْ أَسْمَعُوهُ مَا يَكْرَهُ لَا يَغْضَبُ فَيَكُونُ يُرِيدُ يَنْتَصِرُ لِنَفْسِهِ
1/25 الأمر بالمعروف والنهي عن المنكر للخلال