Narrated Abdullah ibn Zayd:
The Prophet (peace_be_upon_him) intended to do many things for calling (the people) to prayer, but he did not do any of them. Then Abdullah ibn Zayd was taught in a dream how to pronounce the call to prayer. He came to the Prophet (peace_be_upon_him) and informed him. He said: Teach it to Bilal. He then taught him, and Bilal made a call to prayer. Abdullah said: I saw it in a dream and I wished to pronounce it, but he (the Prophet) said: You should pronounce iqamah.