'Voluntary' in the Bible

Imnah the descendant of Levi's son Kore, keeper of the eastern gate, was in charge of voluntary offerings to God, apportioning contributions for the LORD and the most holy things.

His officers contributed a voluntary offering to the people, the priests, and the descendants of Levi. Hilkiah, Zechariah, and Jehiel, the officials who supervised God's Temple, gave 2,600 animals from their flocks to the priests for Passover offerings, along with 300 bulls.