Is it permissible to release an ornamental bird afflicted with a fatal and contagious disease, knowing that it will die whether it is released or kept, and is it preferable to leave it, given the possibility of the infection spreading to the rest of the birds?

If a bird is afflicted with an infectious disease, it should be disposed of, either by releasing it or by killing it if its harm cannot be avoided otherwise. Its killing must be done humanely, by slaughtering it or similar methods, while avoiding burning, as the Prophet (peace and blessings of Allah be upon him) forbade torture by fire.