Prayer: The Merit of Performing Prayer at the Start of Time
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 738
It is recommended that one perform prayers at the start of their prescribed time; this is something that has been highly advised. The nearer to the start of the prescribed time, the better, unless delaying the prayer is better for some reason; for example, someone waits a little to perform the prayer in congregation, on condition that it does not pass the prime time (waqt al‑faḍīlah).[1]
-Ayatullah Sistani, Practical Laws of Islam, Prayer (Salah)
1
This refers to the early period of the prescribed time for a prayer during which there is more reward for performing it.