A prayer between every Azan and Iqamah

Between every Azan and Iqamah there is a voluntary prayer, for whoever wishes.

Narrated by Abdullah ibn Mughaffal

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.

Sahih al-Bukhari 627, Sahih Muslim 838

What this hadith teaches

The "two calls" are the Azan and the Iqamah. Praying two rak'ahs in that gap, even before Maghrib, is a sunnah.

Reference and grade

Grade
Sahih: agreed upon by al-Bukhari and Muslim
Narrator
Abdullah ibn Mughaffal

The hadith in Arabic نص الحديث

بَيْنَ كُلِّ أَذَانَيْنِ صَلاَةٌ بَيْنَ كُلِّ أَذَانَيْنِ صَلاَةٌ ـ ثُمَّ قَالَ فِي الثَّالِثَةِ ـ لِمَنْ شَاءَ

Arabic text of Sahih al-Bukhari 627, as given on sunnah.com.