What is the source of the common quote, "If one comes to kill, arise and kill him first", or in general, the Jewish concept of self-defense?
The concept of “if one comes to kill you, arise and kill him first” (Shmot 22, 1, explained in Brachot 58b) is a most basic moral and Jewish concept, accepted universally by the western world who has adopted the Bible as our objective moral code of action. The most basic and important ideal and mitzvah is to survive. Just like all mitzvot are pushed aside for the saving of the individual (e.g. desecrating Shabbat, eating on Yom Kippur, Rambam, Hil. Shabbat, ch. 2), how much more so are all other factors pushed aside for the self-defense of Am Yisrael, for “The dead cannot praise God” (Tehilim 115, 17), (nor do too much of anything…). This ideal is true regarding all nations, but how much more so regarding a nation designated and obligated to be a moral “light unto the nations” (Yishayau 42, 6), that it’s immoral for us to risk our survival at the moral expense of mankind. From Avraham’s going to war to save his kidnapped nephew from the 4 kings of the north (Breishit 14, 14), to Moshe’s sacrificing his future in Egypt to save his Jewish brother beaten by the Egyptian (Shmot 2, 12), throughout all of sefer Shoftim, Shmuel I and II and M’lachim I and II, down to Megilat Esther, we see that the Book Of Books holds self-defense as the highest of priorities and one of the predominant themes of the Tanach, even one of the central attributes of just about all of the biblical heroes, who were willing to sacrifice their lives for Am Yisrael!