´It was narrated from Jabir, that the Prophet(s.a.w) said:` "There is no soul born upon the earth – meaning today – upon whom will come one hundred years." (Sahih)
Hadith Referenceسنن ترمذي / كتاب الفتن عن رسول الله صلى الله عليه وسلم / 2250
Ibn 'Umar (Allah be pleased with both of them) reported that the Messenger of Allah (ﷺ) had two Mu'adhdhins, Bilal (RA) and son of Umm Maktum, the blind. The Messenger of Allah (ﷺ) said: Bilal (RA) announces Adhan at (the fag end of the) night (i. e. Sahri), so eat and drink till the son of Umm Maktum announces Adhan. And he (the narrator) said: And the (difference of time) between their (Adhans) was not more than this that one climbed down (from the minaret) and the other climbed up (to announce Adhan).
Shaykh Maulana Abdul Aziz Alvi
Hadith Commentary:Benefits and Issues:
➊ The Prophet Muhammad sallallahu alayhi wa sallam had two permanent mu’adhdhins (callers to prayer) for the morning. One of them would give the adhan (call to prayer) at night before dawn so that people could make arrangements and preparations for the morning prayer, and those who had been praying tahajjud (late night voluntary prayer) for a long time could get some rest or relax, and those who intended to fast could make arrangements for fasting. However, this adhan was not for the morning prayer itself. Then, for the morning prayer, Ibn Umm Maktum radi Allahu anhu would give the adhan.
➋ There was not much interval between the two adhans, because its purpose did not require a long time. After Bilal radi Allahu anhu gave the adhan, he would wait a little for the true dawn (subh sadiq), make some supplications and seek forgiveness, and when the time for the rising of the true dawn approached, he would descend from the elevated place and inform Ibn Umm Maktum so that he could prepare to give the morning adhan. Then he would get ready and ascend to the elevated place to give the adhan.
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 2538