Commentary for Yoma 164:1
ורוצח גופיה מנא לן סברא היא דההוא דאתא לקמיה (דרבא) אמר ליה אמר לי מרי דוראי קטליה לפלניא ואי לא קטילנא לך א"ל נקטלך ולא תקטול מאי חזית דדמא דידך סומק טפי דילמא דמא דההוא גברא סומק טפי
Rut whence do we know that this principle applies in the case of a murder? - This is reasonable. For there was a man who came before Raba and said to him: The lord of my village told me: Kill so-and-so, and if you will not, I shall kill you! - He [Raba] answered: Let him kill you, but do not kill! What makes you see that your blood is redder than his? Perhaps the blood of that man is redder than yours?<span class="x" onmousemove="('comment',' The Lord wants you to save your own life, because the life of any one of His children is clear to Him. But your neighbour's life is as clear to Him as your own; and no blood is 'redder than the other'. Hence you must not kill someone else, in order to save life. But if someone comes to murder you, self-defence is not only permissible, but mandatory.');"><sup>1</sup></span> There was a woman with child who had smelt [a dish].