Validity of Salah Prayed with Certainty of Time.

Walekumussalam,

If a person prayed while being fully certain that the prayer time had started, and later it never became clear that he was wrong, then his Salah is valid. He does not have to repeat it.

Because in Hanafi Fiqh, a person is responsible according to his certainty and effort. If no clear mistake is proven later, the prayer remains valid.

 References :

ومن صلى باجتهاده فبان أنه أخطأ فإن تبين أنه 

صلى قبل الوقت لم تجز، وإن لم يتبين شيء أجزأه.

الدر المختار 

Translation:

If someone prayed based on his judgment, then it becomes clear he was wrong — if it is proven that he prayed before the time, the prayer is not valid. But if nothing becomes clear, it is valid for him.

اليقين لا يزول بالشك

 الأشباه والنظائر

Translation:

“Certainty is not removed by doubt.”

If he was sure the time had entered, and no clear proof later shows that it was wrong, then the Salah is valid according to Hanafi Fiqh.