Musnad Ahmad 30:649

Ali ibn Ishaq narrated to us, Abdullah informed us, Yunus informed us, from al-Zuhri, who said: Abu Abdullah al-Agharr informed me that he heard Abu Hurairah saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When it is the day of Friday, there is upon every door [of the mosque]..." and he mentioned it, and he did not doubt regarding the [word] 'egg' (al-baydah).