قَالَ النَّبِيُّ صلى الله عليه وسلم " بَيْنَ كُلِّ أَذَانَيْنِ صَلاَةٌ بَيْنَ كُلِّ أَذَانَيْنِ صَلاَةٌ ـ ثُمَّ قَالَ فِي الثَّالِثَةِ ـ لِمَنْ شَاءَ ".
Abdullah ibn Mughaffal reported: The Prophet ﷺ said, “Between every two calls there is a prayer, between every two calls there is a prayer” – then he said the third time – “for whoever wishes.”
also in Sahih al-Bukhari 624