Is it true that calling the Adhan inside the mosque is an innovation?About the Fajr prayer which Adhan was supposed to be called first, as Salat Kairun Mina Naom or the general one.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Calling the Athaan inside the mosque is permissible if the purpose of the Athaan will be achieved. The purpose is to inform Muslims of the beginning of the times for prayers.

Therefore, calling the Athaan from inside a mosque through a microphone is permissible; it is not an innovation. In the era of the Prophet the Athaan was called from outside the mosque in order to inform the people; it is not a form of worship. Imam Abu Daawood reported in his Sunan on the authority of a woman from Banu An-Najjaar who said: “My house was the loftiest of all the houses around the mosque (of the Prophet ( ), Bilaal used to make the Athaan for the Fajr prayer standing on its roof.”

The words 'prayer is better than sleep' are pronounced in the Athaan that is called after the beginning of Fajr (dawn) since this Athaan is the actual Athaan of Fajr not the Athaan that is called before it. Imam Ahmad narrated in his book Al-Musnad from Abu Mahdhoorah describing the Athaan: “When I call for Fajr prayer, I used to pronounce the words 'prayer is better than sleep.”
According to some narrations, the Athaan of Fajr prayer is named first Athaan since the Iqaamah is called the second Athaan. It is also mentioned in Saheeh Al-Bukhaari and Muslim from the Hadeeth of ‘Abdullah ibn Mughaffal Al-Muzani that the Prophet said: “Between every two Athaans there is prayer.”

For more benefit on calling the Athaan using a microphone, please refer to Fatwa 86904.

Allah knows best.