Allaah says (interpretation of the meaning):
“Verily, As-Salaah (the prayer) is enjoined on the believers at fixed hours”
We have already explained the times of prayer in detail in question no. 9940.
Prayer offered before its time is not valid, according to the consensus of the Muslims. If a person offers a prayer before its time:
-if he does that deliberately, then the prayer is invalid and he is not free of sin.
-If that was not done deliberately, and he did it because he thought that the time for prayer had begun, then it is not a sin, and his prayer is regarded as naafil, but he has to repeat it because one of the conditions of the prayer is that it be done at the right time.
Shaykh Muhammad ibn ‘Uthaymeen, in al-Sharh al-Mumti’, 2/88.