Musnad Ahmad 31:769

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, who said: Al-'Ala' ibn 'Abd al-Rahman narrated to me, from his father, from Abu Sa'id al-Khudri, from the Messenger of Allah (peace and blessings of Allah be upon him) that he said: "When it is the day of Friday, the angels sit at the doors of the mosque and they record the people. Whoever comes of the people, they record them according to their ranks: a man who offered a camel, a man who offered a cow, a man who offered a sheep, a man who offered a chicken, a man who offered a sparrow, and a man who offered an egg." He said: "Then when the caller calls the adhan and the Imam sits on the pulpit, the scrolls are folded, and they enter the mosque to listen to the reminder."