This is another article in the chapter Justice from the classical manual on Sharia called Reliance of the Traveller. The articles are posted one by one in the order they are given in the book.
05.0 THE EXPIATION TO ALLAH FOR TAKING A HUMAN LIFE
05.1 An expiation is due to Allah Most High from anyone who kills someone unlawful to kill, whether the killing is through a mistake or is intentional, and no matter whether retaliation (def: 03) or an indemnity (04) is obligatory or not.
05.2 The expiation consists of freeing a slave (def: k32), or if one cannot, then two consecutive months of fasting. (0: There is no difference in this precedence order whether the killer is legally accountable or not, as when he is a child or insane, in which case the guardian must free a slave on his behalf. (A: Though if a child fasts, it fulfills the expiation.))
05.4 (0: There is no expiation for killing someone who has left Islam, a highwayman (def: 015), or a convicted married adulterer, even when someone besides the caliph kills him.)