Musnad Ahmad 937:107

Ibn Numayr and Ya‘la narrated to us, they said: Al-A‘mash narrated to us, from Zayd ibn Wahb, from Abu Dharr, who said: I was walking with the Prophet, peace and blessings of Allah be upon him, in the mosque. He said: "O Abu Dharr, raise your head and look at the highest man in the mosque." Then he mentioned the hadith.