Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Abu Wa'il and Ibrahim, both of whom say that when the Muslims arrived, they found among the foods of the Magians their breads and their cheese mixed together. All of them ate it, and they did not inquire about it. When cheese was mentioned in the presence of Hazrat Umar, he said: Take the name of Allah over it and eat it.