It is narrated from Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever draws his sword and then uses it, his blood is to be shed with impunity." (That is, by "uses it" is meant that he strikes with it.)
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13879