New Age Islam

In the eighth year of the Hijrah, when the Prophet Muhammad (peace be upon him) conquered the city of Mecca, he gave order to Hazrat Bilal (r.a) to call people to the prayer by performing the Azaan (the call to prayer) from the Ka’bah. He abided by his order and gave the Azaan from the Ka’bah. A Hadith is reported to have mentioned that Hazrat Bilal climbed the roof of the Ka’bah to perform the call to prayer (the Azaan) (2). The mosques of the earliest Muslims including even the Ka’bah lacked the minarets, because they had not yet been invented.

http://newageislam.com/islam-and-spiritualism/nastik-durrani,-new-age-islam/a-historical-account-of-namaz%E2%80%94minaret-%28part-12%29/d/97731