Is it obligatory to repeat the prayer if the worshiper caught the opening takbir and Al-Fatihah before sunrise, then completed it at the time of shuruq (sunrise), or prayed the two rak'ahs of the Fajr sunnah and the obligatory prayer at the time of shuruq? And does intentionally delaying the prayer until its time expires invalidate it?

I began the Fajr prayer before its time expired, so there is no need to repeat it. The obligatory prayer is not forbidden during sunrise; rather, it should be prayed, as the Prophet, peace and blessings be upon him, said: "Whoever forgets a prayer, let him pray it when he remembers it, for there is no expiation for it except that." Some scholars permit praying the Fajr Sunnah (definition) (supererogatory prayer) at sunrise because it is among the prayers with a specific reason. A prayer offered after its time has expired is not invalid but is considered a make-up prayer (qada'). However, it is not permissible to intentionally delay a prayer until its time has expired, for that is a grave disobedience and a major sin.