Yahya reported that a man from the polytheists came to join the Prophet ﷺ in order to fight alongside him. The Prophet said, "Go back." Then they agreed, and he said, "We do not seek the help of a polytheist."
حدثنا مسدد ويحيى بن معين قالا حدثنا يحيى عن مالك عن الفضيل عن عبد الله بن نيار عن عروة
يحيى إن رجلا من المشركين لحق بالنبي ﷺ ليقاتل معه فقال ارجع ثم اتفقا فقال إنا لا نستعين بمشرك
No references are available.
Muslim narrated it in Sahih Muslim, chapters on jihad and expeditions, chapter on the dislike of seeking the help of a disbeliever in warfare unless there is a need for it or he holds a good opinion of the Muslims, hadith 1817, from the hadith of Imam Malik, through this same chain.