Hisnul Muslim · Dua 26 of 267
What to say upon hearing the Athan (call to prayer)
((يَدْعُو لِنَفسِهِ بَيْنَ الْأَذَانِ وَالْإِقَامَةِ فَإِنَّ الدُّعَاءَ حِينَئِذٍ لاَ يُرَدُّ)).
English meaning
One should also supplicate for himself during the time between the athan and the iqamah as supplication at such time is not rejected.