Musannaf Ibn Abi Shayba 3:5064

Abu Bakr narrated to us, he said: Abu Mu’awiyah narrated to us, from ‘Asim, from al-‘Abbas ibn ‘Abd al-Rahman al-Hashimi, who said: The first [instance of] the mosques being perfumed was that the Messenger of Allah (may Allah bless him and grant him peace) saw phlegm in the mosque, so he scraped it off. Then he ordered some *khuluq* (a type of perfume), and he smeared it over the place where it was. He said: So the people began perfuming the mosques.