The Prophet Muhammad (peace and blessings be upon him) used to prohibit soldiers from killing women and children, and he would advise them: {...Do not betray, do not be excessive, do not kill a newborn child.} And he also said: {Whoever has killed a person having a treaty with the Muslims shall not smell the fragrance of Paradisethough its fragrance is found for a span of forty years.}
Also, the Prophet Muhammad (peace and blessings be upon him) has forbidden punishment with fire.
He once listed murder as the second of the major sins, and he even warned that on the Day of Judgment, {The first cases to be adjudicated between people on the Day of Judgment will be those of bloodshed. }
Muslims are even encouraged to be kind to animals and are forbidden to hurt them. Once the Prophet Muhammad (peace and blessings be upon him) said: {A woman was punished because she imprisoned a cat until it died. On account of this, she was doomed to Hell. While she imprisoned it, she did not give the cat food or drink, nor did she free it to eat the insects of the earth.} He also said that a man gave a very thirsty dog a drink, so God forgave his sins for this action. The Prophet (peace and blessings be upon him) was asked, “Messenger of God, are we rewarded for kindness towards animals?” He said: {There is a reward for kindness to every living animal or human.}