Musannaf Ibn Abi Shayba 1:548

Ghundar narrated to us, from Shu'bah, who said: I heard Uthman, the freed slave of Thaqif, narrating from Abu Ziyad, who said: I witnessed Ibn Abbas and Abu Hurairah while they were waiting for a young goat of theirs in the oven. Ibn Abbas said: "Take it out for us, so it does not distract us from the prayer." So they took it out and ate from it. Then Abu Hurairah performed ablution. Ibn Abbas said to him: "Did we eat filth?" Abu Hurairah replied: "You are better than me and more knowledgeable." Then they prayed.