What to say on hearing the Adhan
حَدَّثَنَا إِسْحَاقُ بْنُ رَاهَوَيْهِ، قَالَ حَدَّثَنَا وَهْبُ بْنُ جَرِيرٍ، قَالَ حَدَّثَنَا هِشَامٌ، عَنْ يَحْيَى، نَحْوَهُ. قَالَ يَحْيَى وَحَدَّثَنِي بَعْضُ، إِخْوَانِنَا أَنَّهُ قَالَ لَمَّا قَالَ حَىَّ عَلَى الصَّلاَةِ. قَالَ لاَ حَوْلَ وَلاَ قُوَّةَ إِلاَّ بِاللَّهِ. وَقَالَ هَكَذَا سَمِعْنَا نَبِيَّكُمْ صلى الله عليه وسلم يَقُولُ.
Narrated Yahya as above (586) and added: "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."