Musannaf Ibn Abi Shayba 28:475

Muhammad ibn Bakr narrated to us, from Ibn Jurayj, who said: Ata was asked about a man from the people of the Dhimma (protected non-Muslims) who is caught among the people of Shirk (polytheists), and he says, "I did not intend to aid them against you, and they had stipulated upon me that I would not come to them." He (Ata) disliked killing him except with evidence. He said: And at that time, some of the people of knowledge said to Ata: "If he violates a single thing of what is upon him, then he has violated the peace treaty."