Surah Luqman 31:19
وَٱقْصِدْ فِى مَشْيِكَ وَٱغْضُضْ مِن صَوْتِكَ ۚ إِنَّ أَنكَرَ ٱلْأَصْوَٰتِ لَصَوْتُ ٱلْحَمِيرِ ١٩
EnglishSahih International
And be moderate in your pace and lower your voice; indeed, the most disagreeable of sounds is the voice of donkeys."