What is the first surah that was revealed in its entirety?

Scholars have differed regarding the first complete surah to be revealed from the Qur'an. Al-Suyuti favored that the first complete surah revealed was Al-Muddathir. The different opinions can be reconciled by stating that the beginning of Al-Alaq was revealed first, while Al-Muddathir was revealed completely before it.

It was also said that Al-Fatiha was the first complete surah revealed, but Qadi Abu Bakr deemed this opinion weak.

The different opinions can be reconciled by stating that the first verses revealed were: "Recite in the name of your Lord," and the first command for propagation revealed was: "O you who wraps himself [in clothing]," and the first surah revealed was: Surah Al-Fatiha.

In summary: Scholars differed concerning three surahs (Al-Alaq, Al-Muddathir, and Al-Fatiha) regarding the priority of revelation. However, most scholars tended to believe that Al-Alaq was not revealed completely, leaving the difference of opinion between Al-Muddathir and Al-Fatiha. The most preponderant view is that Al-Muddathir was the first to be revealed completely.