Qur'an 31:19 · Luqman

وَٱقْصِدْ فِى مَشْيِكَ وَٱغْضُضْ مِن صَوْتِكَ ۚ إِنَّ أَنكَرَ ٱلْأَصْوَٰتِ لَصَوْتُ ٱلْحَمِيرِ

(19) And be moderate in your pace and lower your voice; indeed, the most disagreeable of sounds is the voice of donkeys."