How does one perform the Sunnah prayer while sleeping or sitting?

If the questioner wishes to know how to perform supererogatory (nafl) prayers while sitting, it means performing the known form of the nafl prayer but sitting instead of standing. One would then gesture for rukoo' (bowing) from the sitting position and perform normal sujood (prostration). However, the reward is reduced by half for one who has no valid excuse. As for performing nafl prayers while reclining, it means performing them while leaning back, but sitting up for rukoo' and sujood.

It is reported in At-Tirmidhi, on the authority of Imran ibn Husayn, that the Messenger of Allah, peace and blessings be upon him, said concerning a man's prayer while sitting: "He who prays standing, that is better. And he who prays sitting, for him is half the reward of one who prays standing. And he who prays lying down, for him is half the reward of one who prays sitting."

Al-Khattabi and Ibn Battal are of the view that one who is able to stand should not perform supererogatory prayers by gesturing (for rukoo' and sujood). However, Al-Iraqi holds that it is permissible, based on a difference of opinion between the Shafi'is and Malikis. He mentioned two views within the Shafi'i madhhab, one of which is validity. And within the Maliki madhhab, there are three views, one of which is absolute permissibility in cases of necessity and choice.

In "Tuhfat al-Muhtaj," it is permissible by scholarly consensus for one who is able to perform supererogatory prayers while sitting. Similarly, it is permissible while reclining, according to the more correct opinion, and it is preferable to be on the right side. One who is reclining must sit up for rukoo' and sujood. As for lying on one's back, it is not valid if reclining is possible.