Musnad Ahmad 435:35

Ya'la and Yazid ibn Harun narrated to us, they said: Mujammi' ibn Yahya al-Ansari narrated to us, he said: I was beside Abu Umamah ibn Sahl, and he was facing the mu'adhdhin. The mu'adhdhin said the takbir twice, so Abu Umamah said the takbir twice. He testified that there is no god but Allah twice, so Abu Umamah testified twice. The mu'adhdhin testified that Muhammad is the Messenger of Allah twice, so Abu Umamah testified twice. Then he turned to me and said: "Thus did Mu'awiyah ibn Abi Sufyan narrate to me, from the Messenger of Allah, peace and blessings of Allah be upon him."