What is the expiation for leaving a mouse to die of hunger and thirst?

There is no sin in killing mice, as they are among the pests that may be killed both inside and outside the sacred precincts (Haram). However, it is not permissible to leave them confined until they die, as this constitutes torture, which contradicts the excellence (ihsan) commanded by the Prophet, peace and blessings be upon him, when killing. There is no specific expiation for the husband, but he must seek forgiveness and strive for excellence in killing in the future.