Musannaf Ibn Abi Shayba 1:1558

Ghundar narrated to us, from Ibn Jurayj, from ‘Ata’, regarding the saying of the Exalted: “...nor [when you are] in a state of janabah (major ritual impurity), except those passing through [a place of] transit.” He said: The person in a state of janabah may pass through the mosque.