Abdullah bin Zayd (r.a.)
Hz. Abdullah was of Ansar. He took part in the Pledge of Aqabah. He was adherent to the Messenger of Allah with his whole heart. He took part in all battles with the Prophet. He fought heroically. He carried the flag of Sons of Harith of the tribe of Khazraj during the Conquest of Makkah
Abdullah is known as “Sahibul-Adhan”. This name was given to him because he saw adhan in his dream exactly before adhan was known as call to prayer. This incident took place as follows:
It was just after the Migration. People used to shout “As-Salatu Jami'ah” to call people to prayer. The Prophet talked to the Companions to find something more appropriate. He said, “I want all Muslims to perform prayers together.” He asked them their opinions about it. Some Companions suggested ringing bells but the Prophet rejected it saying, “It is the custom of Christians.” Others suggested blowing a horn but the Messenger of Allah said, “It is the custom of Jews.” They could not agree on anything.
Each of the Companions that were there thought about the issue that day. Sleeping with this idea in his mind, Hz. Zayd, saw a man wearing green garments in his dream. He had a bell in his hand. Hz. Zayd asked him to sell him the bell. The man said, “What are you going to do with it?” Zayd said, “I will use it to inform people about prayer times.” The man said, “I will describe you something better.” Then, he turned toward the qiblah, recited adhan in the same way as it is called to day. When he repeated it, he added the sentence, “Qad qamatis-salah”. Then, he disappeared.
Hz. Abdullah woke up in excitement. He was still under the influence of the dream. He waited for an appropriate time. Then, he entered into the presence of the Messenger of Allah. He informed him about the dream he had. The Prophet (pbuh) said, “The dream is true. Teach those words to Bilal so that he will recite them.” Hz. Abdullah taught adhan to Hz. Bilal. Hz. Bilal ascended to a high place and called the first adhan. A few people who heard it came and said they had seen the same thing in their dreams. Then, revelation about adhan was sent down to the Messenger of Allah. The story of adhan that has been called since the first year of the Migration as a sign of Islam is like that. Today, adhan that is called five times a day is a memory of Hz. Abdullah bin Zayd.
Hz. Abdullah was famous for his generosity. He was together with the Prophet in the Farewell Hajj. He gave all of his property and animals away as sadaqah to the poor during this hajj. He preferred to live in financial difficulty. Hz. Abdullah died in 22 H during the caliphate of Hz. Uthman. 
May Allah be pleased with him!
Tabaqat, 1: 246-247; 3: 536; Musnad, 4: 42.