Sura al-Baqara 2:91

وَإِذَا قِيلَ لَهُمْ ءَامِنُوا۟ بِمَآ أَنزَلَ ٱللَّـهُ قَالُوا۟ نُؤْمِنُ بِمَآ أُنزِلَ عَلَيْنَا وَيَكْفُرُونَ بِمَا وَرَآءَهُۥ وَهُوَ ٱلْحَقُّ مُصَدِّقًا لِّمَا مَعَهُمْ قُلْ فَلِمَ تَقْتُلُونَ أَنۢبِيَآءَ ٱللَّـهِ مِن قَبْلُ إِن كُنتُم مُّؤْمِنِينَ

wa-idhā qīla lahum āminū bimā anzala allāhu qālū nuʾminu bimā unzila ʿalaynā wa-yakfurūna bi-mā wa-rāʾahu wa-huwa l-ḥaqqu muṣaddiqan li-mā maʿahum qul falima taqtulūna anbiyāʾa allāhi min qablu in kuntum muʾminīna

When it is said to them, "Believe in what Allah Hath sent down, "they say, "We believe in what was sent down to us:" yet they reject all besides, even if it be Truth confirming what is with them. Say: "Why then have ye slain the prophets of Allah in times gone by, if ye did indeed believe?"