Sahih al-Bukhari Book 10, Hadith 11
"Some of my companions told me that Hisham had said, "When the Mu'adh-dhin said, "Haiyi `alassala
(come for the prayer)." Muawiya said, "La hawla wala quwata illa billah (There is neither might
nor any power except with Allah)" and added, "We heard your Prophet saying the same."
that he had heard Muawiya repeating the words of Adhan up to "Wa ash-hadu anna Muhammadan rasulul-lah (and I testify that Muhammad is Allah's Messenger (ﷺ).)"
Allah's Messenger (ﷺ) said, "Whoever after listening to the Adhan says, 'Allahumma Rabba hadhihi-dda` watit-tammah, was-salatil qa'imah, ati Muhammadan al-wasilata wal-fadilah, wa b`ath-hu maqaman mahmudan-il-ladhi wa`adtahu' [O Allah! Lord of this perfect call (perfect by not ascribing partners to You) and of the regular prayer which is going to be established, give Muhammad the right of intercession and illustriousness, and resurrect him to the best and the highest place in Paradise that You promised him (of)], then my intercession for him will be allowed on the Day of Resurrection".