It was narrated that ‘Abdur-Rahman bin Abi Laila said:
When `Ali bin Abi Talib (رضي الله عنه) heard the mu`addhin giving the adhan, he used to repeat after him. When he said, I bear witness that there is no god but Allah and I bear witness that Muhammad is the Messenger of Allah (ﷺ), `Ali (رضي الله عنه) would say: I bear witness that there is no god but Allah and I bear witness that Muhammad is the Messenger of Allah (ﷺ), and that those who deny Muhammad are the liars.