"I was with Mu'awiyah when the Mu'adhdhin called the Adhan. Muawiyah said what the Mu'adhdhin said, but when he said: 'Hayya 'alas-salah (come to prayer),' he said: 'La hawla wa la quwwata illa Billah (There is no power and no strength except with Allah);' and when he said: 'Hayya 'alal-falah (come to prosperity),' he said: 'La hawla wa la quwwata illa Billah (There is no power and no strength except with Allah).' After that he said what the Mu'adhdhin said, then he said: 'I heard the Messenger of Allah ﷺ saying exactly like that.'" (Using translation from Nasāʾī 677)  

إِنِّي لَعِنْدَ مُعَاوِيَةَ إِذْ أَذَّنَ مُؤَذِّنُهُ فَقَالَ مُعَاوِيَةُ كَمَا قَالَ الْمُؤَذِّنُ حَتَّى إِذَا قَالَ حَيَّ عَلَى الصَّلَاةِ قَالَ لَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِاللهِ فَلَمَّا قَالَ حَيَّ عَلَى الْفَلَاحِ قَالَ لَا حَوْلَ وَلَا قُوَّةَ إِلَّابِاللهِ وَقَالَ بَعْدَ ذَلِكَ مَا قَالَ الْمُؤَذِّنُ ثُمَّ قَالَ سَمِعْتُ رَسُولَ اللهِ ﷺ قَالَ ذَلِكَ  

[Machine] I heard the Messenger of Allah ﷺ say repeatedly, when the Mu'adhin (caller to prayer) calls the Adhan, and then he pronounces the Shahada (testimony of faith), the Messenger of Allah ﷺ would also pronounce the Shahada. And when he says "Hayya 'ala As-Salah" (come to prayer), he would say "La hawla wa la quwwata illa Billah" (there is no might or power except with Allah). And when he says "Hayya 'ala Al-Falah" (come to success), he would also say "La hawla wa la quwwata illa Billah" (there is no might or power except with Allah).  

سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ مِرَارًا إِذَا أَذَّنَ الْمُؤَذِّنُ فَتَشَهَّدَ تَشَهَّدَ رَسُولُ اللهِ ﷺ كَمَا يَتَشَهَّدُ فَإِذَا قَالَ حَيَّ عَلَى الصَّلَاةِ قَالَ «لَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِاللهِ» فَإِذَا قَالَ حَيَّ عَلَى الْفَلَاحِ قَالَ أَيْضًا «لَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِاللهِ»