Musannaf Ibn Abi Shayba 1:1552

Sharik ibn Abdullah narrated to us, from Abd al-Karim, from Abu Ubaydah, who said: The *junub* (person in a state of major ritual impurity) may pass through the mosque but not sit in it. Then he recited: "Nor [should you approach prayer] when you are in a state of major impurity, except when passing through [the mosque]."