The supererogatory prayer with a single rak'ah is Salatul
Answer Details
The supererogatory prayer with a single rak'ah is Salatul Witr. This prayer is usually performed after the obligatory night prayer (Isha) and before the break of dawn (Fajr). It is an optional prayer and can be performed at any time of the night. Salatul Witr consists of one rak'ah, which includes recitation of surah Al-Fatihah and any other surah from the Quran, followed by bowing, standing up, prostrating and sitting in a manner similar to other prayers.