"We were with the Messenger of Allah (S.A.W) and Bilal stood up and gave the call. When he fell silent the Messenger of Allah (ﷺ) said: 'Whoever says the same as this (what the Mu'adhdhin) with certainty, he will enter Paradise.
Sunan an-Nasa'i Book 7, Hadith 49
← Previous Hadith "When you hear the call, say what the Mu'adhdhin says."

Sunan an-Nasa'i Book 7, Hadith 48 Next Hadith → "I was sitting with Abu Umamah bin Sahl bin Hunaif when the Mu'adhdhin called the Adhan. He said: 'Allahu akbar; Allahu Akbar (Allah is the Greatest, Allah is the Greatest),' and he (also) pronounced the takbir twice. Then he said: 'Ashhadu an la ialaha ill-Allah (I bear witness that there is none worthy of worship except Allah),' and he also sent the testimony twice. Then he said: 'Ashhadu anna Muhammadan Rasul-Allah (I bear witness that Muhammad is the Messenger of Allah),' and he (also) sent the testimony twice. Then he said: 'This is what Mu'awiyah bin Abi Sufyan told me, narrating from statement of the Messenger of Allah (S.A.W).'"

Sunan an-Nasa'i Book 7, Hadith 50