Sunan at-Tirmidhi (Jami-al-Tirmidhi), Chapter: Salah (Prayers)

his father as saying that when it was morning they went to Allah's Messenger (SAW) and told him about the dream. He said, "This is a true dream. Stand up with Bilal. He has a louder voice than you. Teach him that which you were told and he will call that out. "When Umar ibn al-Khattab (RA) heard Bilal's call to prayer, he came to Allah's Messenger (SAW) dragging his garment along and he said, "O Messenger of Allah! By Him who sent you with Truth, I have seen the like of what he says. "So, Allah's Messenger (SAW) said, "All praise belongs to Allah, and that is confirmed." [Ahmed 16478, Ibn Majah 1706, Abu Dawud 499]