Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1822
Abdullah b. Mughaffal reported Allah's Messenger (may peace be upon him) u saying: There Is between the two calls (Adhan and Iqama) a prayer. And he mentioned it three times, and at the third time he said: This applies to those who wish to do it.