Is it permissible to combine the regular Sunnah prayers (12 rak'ahs) into a single prayer?

The Shari'ah has specified particular times for the obligatory prayers and has legislated supererogatory (Sunnah) prayers before or after them. The time for the supererogatory prayers performed before the obligatory prayer begins with the entry of the time for the obligatory prayer. The time for those performed after the obligatory prayer begins with the performance of the obligatory prayer. The time for both continues until the time for the obligatory prayer exits. Therefore, performing the supererogatory prayers all at once before their designated time is not sufficient. Delaying them beyond their time and making them up all at once is contrary to what is superior, and some scholars do not legitimize making up supererogatory prayers after their time has exited.