It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you points his spear at a man, and even if its head has reached the hollow of his throat, and he says: La ilaha illa Allah (there is no god but Allah), then let him withdraw the spear from him."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10254