If a person begins their prayer while having doubt (Shakk) about whether the time has entered, and subsequently discovers that the time had indeed entered, what is the legal status of their prayer?

Conditions of Prayer Part 3: Time, Intention, and Opening Takbir

• The prayer is fully valid because the timing was correct.
• The prayer is null and void because of the initial doubt.
• Only the sunnahs must be repeated.
• Draining water is required.