It is narrated from Abdullah bin Sa’d, the freed slave of Umar bin Khattab (may Allah be pleased with him), that Umar (may Allah be pleased with him) said: "The Arabs who are Christians are not among the People of the Book, and the animals they slaughter are not lawful for us, and I will not leave them until they accept Islam or I will strike their necks."
Hadith Referenceمسند الإمام الشافعي / كتاب الأطعمة والصيد والذبائح / 1532
Hadith Takhrijاسناده ضعیف، لضعف شيخ الشافعي اخرجه البيهقي : 9 / 216، 284 - وفي المعرفة السنن والآثار له (5553)۔