Sahih al-Bukhari 127
Sahih al-Bukhari · Book 3: Knowledge · Whoever selected some people to teach them (religious) knowledge preferring them over others for fear that the others may not understand it
وَقَالَ عَلِيٌّ حَدِّثُوا النَّاسَ، بِمَا يَعْرِفُونَ، أَتُحِبُّونَ أَنْ يُكَذَّبَ، اللَّهُ وَرَسُولُهُ؟ حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُوسَى عَنْ مَعْرُوفِ بْنِ خَرَّبُوذٍ عَنْ أَبِي الطُّفَيْلِ عَنْ عَلِيٍّ بِذَلِكَ .
And ‘Ali said, “You should preach to the people according to their mental caliber so that they may not convey wrong things about Allah and His Messenger ﷺ.” Abu at-Tufail narrated the above mentioned statement of `Ali.