When is the time for the call to prayer (Adhan) valid?

Primary text

The Adhan is valid only after the entrance of the prescribed time for the prayer, with the exception of the Fajr prayer. There is no known disagreement on this ruling. Scholars have reached a consensus that it is Sunnah to give the Adhan for all prayers only after their time has begun. This is because the Adhan is legislated to announce the time; issuing it beforehand would negate its intended purpose.