Reference for Pesachim 50:4

ושפיכות דמים גופיה מנלן סברא הוא כי ההוא דאתא לקמיה דרבא א"ל מרי דוראי אמר לי זיל קטליה לפלני' ואי לא קטלינא לך א"ל ליקטלוך ולא תיקטול מאי חזית דדמא דידך סומק טפי דילמא דמא דההוא גברא סומק טפי

Even as one who came before Raba and said to him: The governor of my town has ordered me, 'Go and kill So-and-so, if not, I will kill you.' He answered him: 'Let him kill you rather than that you should commit murder; what [reason] do you see [for thinking] that your blood is redder? Perhaps his blood is redder.'<span class="x" onmousemove="('comment',' You have no right to murder him to save yourself; his life is no less valuable than your own.');">⁷</span>

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