Calling aathaan inside the masjid or prayer room
Question

                Is it against the Sunnah to call the adhan inside the Musallah? I believe the 
way of the Salaf is to call it from the tallest structure/house near the masjid or 
the masjid itself.
Praise be to Allah.Al-hamdu lillaah.
There is absolutely nothing wrong with calling the athaan in the musallah; on the 
contrary, it is better than abandoning it altogether. Prophet Muhammad  (peace be 
upon him) taught two men who were traveling how to make the call for prayer while 
traveling, where no mosques or musallahs may be found. As was narrated in the 
hadeeth saheah by Malik Ibn Al-Huwayrith: "My cousin and I came to the Prophet 
SAWS and he said to us, ‘If you travel, (meaning while you are traveling) perform the 
call for prayer, and call the iqamah before prayer and let the older one of you be the 
Imam." Narrated by Al Bukhari, Fath ul-Baari hadeeth #658 and Al Tirmidhi, hadeeth 
#189. According to Abu Eissa (Al Tirmidhi) this hadeeth is hasan saheeh. There were 
two views on the hadeeth. The majority of the Muslim scholars agreed on the validity of 
calling the aathaan while traveling. Others however, have said that the iqamah alone is 
sufficient, and that the purpose of the aathaan is to gather people for prayer. According 
to Ahmad and Ishaaq, the first view is more sound. 
In another Hadeeth narrated by ‘Ukbah bin ‘Aamir he said: I heard the Prophet  say, 
"Allaah is pleased by a shepherd who, while on the top of a mountain, calls for prayer 
and prays. Allaah the Almighty says, ‘Look at my worshipperhe calls the aathaan, 
and he prays; he fears me. I have forgiven my worshipper, and I have sent him to 
heaven ( meaning that Allah chose for this person to go to heaven).’" Narrated by 
Al-Nisaa’i, Abu Dawood, and Ahmad and was confirmed sound by Al Albany in his 
book Saheeh Al-Jami’, Hadeeth #8102.
The benefits of the aathaan are many and they are by no means limited to gathering 
people, or announcing prayer time. They encompass: repelling Satan, getting rewarded 
in the afterlife for calling for prayer, and furthermore, for announcing and repeating the 
oneness of Allaah, etc. 
Allaah knows best.