Sunan Abi Dawud Book 2, Hadith 107
Hisham ibn Sa'd reported: We entered upon Mu'adh ibn Abdullah ibn Khubayb al-Juhani. He said to his wife: When (at what age) should a boy pray? She replied: Some person of us reported: The Messenger of Allah (ﷺ) was asked about it; he said: When a boy distinguishes right hand from the left hand, then command him to pray.
Waki' misunderstood the name of Dawud b. Sawar. Abu Dawud al-Tayalisi has narrated this tradition from him. He said: Anu Hamzah Sawar al-Sairafi.
AbuUmayr reported on the authority of his uncle who was from the Ansar (the helpers of the Prophet): The Prophet (ﷺ) was anxious as to how to gather the people for prayer.
The people told him: Hoist a flag at the time of prayer; when they see it, they will inform one another. But he (the Prophet) did not like it. Then someone mentioned to him the horn.
Ziyad said: A horn of the Jews. He (the Prophet) did not like it. He said: This is the matter of the Jews. Then they mentioned to him the bell of the Christians. He said: This is the matter of the Christians. Abdullah ibn Zayd returned anxiously from there because of the anxiety of the Apostle (ﷺ). He was then taught the call to prayer in his dream. Next day he came to the Messenger of Allah (ﷺ) and informed him about it.
He said: Messenger of Allah, I was between sleep and wakefulness; all of a sudden a newcomer came (to me) and taught me the call to prayer. Umar ibn al-Khattab had also seen it in his dream before, but he kept it hidden for twenty days.
The Prophet (ﷺ) said to me (Umar): What did prevent you from saying it to me?
He said: Abdullah ibn Zayd had already told you about it before me: hence I was ashamed.
Then the Messenger of Allah (ﷺ) said: Bilal, stand up, see what Abdullah ibn Zayd tells you (to do), then do it. Bilal then called them to prayer.
AbuBishr reported on the authority of AbuUmayr: The Ansar thought that if Abdullah ibn Zayd had not been ill on that day, the Messenger of Allah (ﷺ) would have made him mu'adhdhin.