Musnad Ahmad 834:35

Yazid narrated to us, informed us al-Jurayri and Kahmas, from Abdullah ibn Buraydah, from Abdullah ibn Mughaffal, who said: The Messenger of Allah, peace and blessings of Allah be upon him, 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."