Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.103.

Section : Whoever Makes the Azhan May Make the Iqamah.

This is so because the caller to prayer takes precedence in making the iqamah. Says Ash-Shaifi, “If a man made the azhan, he should follow it up with the iqamah.” Of this, at-Tirmizhi says, “Most of the scholars agree with this opinion.”