Musannaf Ibn Abi Shayba 3:5006

Waki’ narrated to us, from Kahmas, from Ibn Buraydah, from Abdullah ibn al-Mughaffal, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Between every two calls (Adhan and Iqamah) is a prayer; between every two calls is a prayer; between every two calls is a prayer, for whoever wishes."