What is the ruling on expelling small kittens from an apartment a short time after their birth, causing them to be lost? And is that considered a sin requiring expiation?

Allah Almighty commanded gentleness in all things, and whoever is deprived of gentleness is deprived of good. Those who own animals must protect them, feed them, and give them water. It is not permissible to expose them to perdition, for a woman entered Hellfire because of a cat she imprisoned.

Similarly, the Messenger of Allah, peace and blessings be upon him, forbade distressing a bird by taking its young and commanded that its chicks be returned to their mother.

The summary of the matter is that whoever Allah entrusts with any animal, must care for it, treat it kindly, and be gentle with it.

Accordingly, one must repent to Allah Almighty for disobeying parents, and for neglecting the care of the cats, which led to their demise, and for distressing their mother by the death of her kittens.

Although feeling guilty indicates a living heart, excessive despair and hopelessness are not permissible, for Allah says: (Say, "O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful"). Allah accepted the repentance of a man who killed a hundred souls, so there is no despair from Allah's forgiveness and mercy. Let good deeds erase bad deeds.