Shaykh Ibn Uthaymeen was asked:
Is it permissible to pray the Sunnah ar-Raatibah that come before the prayer before the adhan?
“It is not permissible. The Sunnah ar-Raatibah that are before the prayer must be after the time enters. If a person prayed the Sunnah ar-Raatibah before the time entered even for a second/moment, it does not count as the Raatibah. Rather it is necessary for him to repeat it.
In this occasion, I would like to bring attention to a danger issue. It is [regarding] the Fajr prayer. The mu’adhins call the adhan before the time and sometimes they call the adhan before the time [enters] by five or six minutes. So some people come, especially in the days of fasting, and hasten and pray. This is very dangerous. If he makes the opening Takbeer before the time enters, then his prayer is not valid and he did not discharge/fulfill his responsibility. Even though it is correct as a voluntary prayer, he did not discharge/fulfill his responsibility. So like that, it is necessary for the Fajr prayer and its Sunnah to be delayed at least ten minutes after the adhan until we are certain or most likely think that the time has entered”.
[al-Liqa’aat ar-Ramadaaniyyah (pg. 161)]
Faisal bin Abdul Qaadir bin Hassan