Imam al-Shafi'i (may Allah have mercy on him) said: What is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) about their slaughtered animals being lawful comes only through the narration of Ikrimah.
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) was asked about the slaughtered animals of the Christians of the Arabs, and he made a statement which was reported as declaring them lawful, and he recited this verse: "And whoever among you befriends them is indeed one of them." [Surah al-Ma'idah: 51] But Malik bin Anas (may Allah have mercy on him) did not mention the name of Ikrimah, and Thawr did not meet Ibn Abbas (may Allah be pleased with them both).
The Shaykh (may Allah have mercy on him) said: Malik bin Anas (may Allah have mercy on him) did not mention Ikrimah in most of the narrations from him, as though he did not consider him fit to be used as evidence; and Thawr al-Dili narrated it only through him (Ikrimah) from Ibn Abbas (may Allah be pleased with them both), so it should not be used as evidence, and Allah knows best. This is what Ibn Abbas (may Allah be pleased with them both) said in what Ikrimah narrated from him, and we have turned away from it only because of the statement of Sayyiduna Umar and Sayyiduna Ali (may Allah be pleased with them both).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18804