Anas b. Malik reported:They (the Companions) discussed that they should know the timings of prayer by means of something recognized by all. Some of them said that fire should be lighted or a bell should be rung. But Bilal was ordered to repeat the phrases twice in Adhan, and once in Iqama
Opening the collection...
“Read in the name of your Lord who created.” 96:1
“My Lord, increase me in knowledge.” 20:114
“So remember Me; I will remember you.” 2:152
“Indeed, with hardship comes ease.” 94:6