Qabus bin Abi Zabyan narrates from his father that Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: None but a Muslim should slaughter your sacrifice, and when he slaughters, say: 'Bismillah, Allahumma minka wa laka' (In the name of Allah; O Allah, it is from You and for You). O Allah, accept it from so-and-so.
Imam al-Shafi'i (may Allah have mercy on him) said: If a polytheist whose slaughtered animal is lawful slaughters the sacrifice, it is valid, though I dislike it.
Al-Shaykh (may Allah have mercy on him) said: That is because their slaughtered animals are also lawful.
(b) Ata bin Abi Rabah (may Allah have mercy on him) said: There is no harm in it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19168