وَإِذَا قِيلَ لَهُمْ ءَامِنُوا۟ بِمَآ أَنزَلَ ٱللَّهُ قَالُوا۟ نُؤْمِنُ بِمَآ أُنزِلَ عَلَيْنَا وَيَكْفُرُونَ بِمَا وَرَآءَهُۥ وَهُوَ ٱلْحَقُّ مُصَدِّقًا لِّمَا مَعَهُمْ ۗ قُلْ فَلِمَ تَقْتُلُونَ أَنۢبِيَآءَ ٱللَّهِ مِن قَبْلُ إِن كُنتُم مُّؤْمِنِينَ Qur’an Al-Baqara (2:91)Waitha qeela lahum aminoo bima anzala Allahu qaloo numinu bima onzila AAalayna wayakfuroona bima waraahu wahuwa alhaqqu musaddiqan lima maAAahum qul falima taqtuloona anbiyaa Allahi min qablu in kuntum mumineena
A reference to their assertion that they believe in what has been revealed to them - i.e., the Law of Moses, which obviously prohibits the killing not only of prophets but of any innocent human being. See also the concluding sentences of verses {61} and {87}, and the corresponding notes.
Even the race argument is often flimsy and hollow pretext. Did not the Jews reject Prophets of their own race who told them unpleasant truths? And do not other nations do likewise? The real trouble is selfishness, narrowness, a mean dislike of anything which runs counter to habits, customs or inclinations.