Answered by Ustadh Salman Younas
Question: How soon can you pray isha after maghrib? If I look outside and it looks completely dark, can I pray isha even if it isn’t “in” yet?
Answer: assalamu `alaykum
It would not be valid to perform a prayer before the entrance of its time.
The Qur’an states, “Prayer at fixed times has been enjoined upon the believers.” (4:103) This is decisive evidence that (a) prayer is obligatory and (b) this obligation relates to specific times.
Someone who performs an obligatory prayer before its time without a valid excuse would have to repeat that prayer. I would advise you to rely on a prayer calendar to determine when the time for a particular prayer enters.
Checked & Approved by Shaykh Faraz Rabbani