يَدْعُو لِنَفْسِهِ بَيْنَ الأَذَانِ وَالإِقَامَةِ؛ فَإنَّ الدُّعَاءَ حِيْنَئذٍ لَا يُرَدُّ.

One should also supplicate for himself during the time between the adhān and the iqāmah as supplication at such time is not rejected.

Reference: Al-Tirmidhī (#212), Abū Dāwud (#521), and Aḥmad (3/119). Also see Irwāʾ al-Ghalīl (1/262).