Musnad Ahmad 288:23

Abu Ahmad al-Zubayri narrated to us, he said: Sufyan narrated to us, from Abdullah ibn Isa, from Yahya ibn al-Harith, from Abu al-Ash'ath al-San'ani, from Aws ibn Aws al-Thaqafi, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever performs ghusl and causes ghusl to be performed, then goes early and arrives at the beginning, and sits near the Imam, and listens and remains silent, he shall have for every step the reward of a year of fasting and praying."