"A shepherd boy should be dressed in uniform, and a soldier should herd sheep" comes from which poem, what is its title and who is its author?

The name seems to be Qingzhou pastoral.

The whole poem is as follows:

Born in a deep valley, I love looking up to the sky, and I just want to climb mountains. I just want to turn Peng Yan into a wild goose in my life, flapping my wings at the edge of the sky and clouds. Thirty years later, I wandered around. Thirty years ago, I was a shepherd. Shepherd boys should be subdued, and soldiers should herd sheep.