What is the evidence from the Quran and the Sunnah that it is legitimate to perform one voluntary prayer with several intentions? For example, is it sound to perform a two-Rak'ah (unit of prayer) prayer intending the voluntary prayer after Wudhoo' (ablution), Tahiyyat-ul-Masjid and the pre-Thuhr (noon) voluntary prayers?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His Slave and Messenger.

The scholars stated that Tahiyyat-ul-Masjid (prayer upon entering the masjid) and the voluntary prayer after Wudhoo' are not intended as independent prayers. Rather, what is intended is to perform a prayer after Wudhoo' and before sitting down upon entering the mosque. Performing any other prayer, obligatory or voluntary, is enough for both in this regard.

An-Nawawi said: "When one enters the prayer intending both an obligatory prayer and Tahiyyat-ul-Masjid, his prayer is valid and sufficient for both. Shaafi'i scholars unanimously agree in this regard, and they explicitly stated that there is no difference of opinion about the prayer being sufficient for both…" until he said: "It is not conditioned that one intends Tahiyyat-ul-Masjid. Rather, when he prays with the intention of praying a prayer, whether that is a confirmed or an unconfirmed voluntary prayer; an obligatory prayer, during or after its fixed time; or a prayer for fulfilling a vow; then his prayer is sufficient, and Tahiyyat-ul-Masjid is implicitly performed, and there is no argument in this regard."

This is what the scholars have deduced and the evidence for the Tahiyyat-ul-Masjid prayer is the Hadeeth where the Prophet said: "When one of you enters the mosque, he should perform a two Rak'ah prayer before he sits down." [Al-Bukhari and others]

The scholars deduced from this Hadeeth that performing two Rak'ahs of prayer before sitting down in the mosque is what is intended, regardless of them being obligatory or voluntary.

The evidence for the voluntary prayer after Wudhoo' is the Hadeeth of the Prophet where he said to Bilal : "O Bilal, tell me about the most hopeful act (which you deem the most rewarding with Allaah) you have done since you accepted Islam, because last night I heard the sound of your footsteps in front of me in Paradise." Bilal said: "I do not consider any act more hopeful in my Islam than that whenever I make ablution (or take a bath) in any hour of the night or day, I would immediately perform prayer for as long as it was destined for me to pray." [Muslim and others]

Allaah Knows best.