When ʿAli bin Abi Talib ؓ heard the muʿaddhin 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, ʿAli ؓ 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.
أَنَّ مُحَمَّدًا رَسُولُ اللهِ قَالَ عَلِيٌّ أَشْهَدُ أَنْ لَا إِلَهَ إِلا اللهُ وَأَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ اللهِ وَأَنَّ الَّذِينَ جَحَدُوا مُحَمَّدًا هُمِ الْكَاذِبُونَ