1 Chronicles 25:7

So the number of them, with their brethren
Who each of them had twelve with them, as after reckoned: that were instructed in the songs of the Lord;
taught how to sing them: [even] all that were cunning;
expert and well skilled in the science of singing: was two hundred and eighty eight;
for there being twenty four classes answerable to those of the priests, and twelve in each class, twelve times twenty four makes two hundred and eighty eight.