What is the ruling on intentionally killing a sparrow with stones in the early period of puberty, and what is the expiation for that?

Killing a sparrow intentionally with stones is unlawful (haram), due to the Prophet's (peace be upon him) prohibition against using living beings as targets, his command to show excellence when slaughtering, and the consensus of scholars on the impermissibility of killing edible animals without benefit. The one who commits this act must repent to Allah and regret what they have done, and there is no specific expiation required of them.