TSK · Numbers 18:17

He shall lay his hand on the head of his offering, and kill it at the door of the Tent of Meeting: and Aaron's sons, the priests shall sprinkle the blood around on the altar.

All the firstborn males that are born of your herd and of your flock you shall sanctify to Yahweh your God: you shall do no work with the firstborn of your herd, nor shear the firstborn of your flock.