Musnad Ahmad 937:259

'Affan narrated to us, Mahdi narrated to us, Wasil narrated to us, from Yahya ibn 'Aqil, from Yahya ibn Ya'mar—and Wasil would sometimes mention Abu al-Aswad al-Du'ali—from Abu Dharr, from the Prophet, peace and blessings of Allah be upon him, who said: "The deeds of my nation were presented to me, their good ones and their bad ones. I found among the good of their deeds the removal of an obstacle from the road. And I found among the bad of their deeds the phlegm that is in the mosque and is not buried."