Abu Huraira reported God’s Messenger as saying, “If anyone helps in killing a believer to the extent of half a word,* he will meet God with ‘Despairing of God’s mercy’ written on his forehead.” Ibn Majah transmitted it. * This is taken to mean that it is a serious matter even to utter half the word which expresses an intention to kill a believer.
Reported by Ibn Majah (No. 2620). Cited in Mishkat al-Masabih (No. 3484).