1 Chronicles 25:19

The twelfth to Hashabiah, he, his sons, and his brethren, were twelve:

The twelfth lot in the musical division belonged to a larger moment when David brought to completion the ordering of every department of national life — priestly, Levitical, civil, and military — as Solomon was about to ascend the throne. That organization was not improvised, for David had diligently studied the divine pattern of assigning distinct duties to those most qualified for them, and he made that pattern the rule of his administration of Israel. In keeping with it, the four thousand appointed to praise the Lord upon instruments were arranged into twenty-four rotating courses.

Each course consisted of twelve men serving under leaders who had been specially trained and were highly skilled in handling musical instruments. Hashabiah, together with his sons and his kinsmen, constituted the twelfth of those twelve-man courses.