Praying voluntary prayers sitting or standing

The scholars agree that it is permitted to perform voluntary prayer sitting while able to stand, for voluntary prayer is a lasting good, and requiring it standing would prevent that good from being maintained (Sharh Muslim, 6/10; al-Majmu', 3/231; Bada'i' al-Sana'i', 1/297; al-Bahr al-Ra'iq, 2/67; Hashiyat al-Tahtawi, 1/265; Hilyat al-Ulama, 2/120; al-Majmu', 3/232; Fath al-Bari, 2/585; Umdat al-Qari, 7/160; Durr al-Hukkam, 2/30; Nihayat al-Muhtaj, 1/471; Nayl al-Awtar, 3/99). And because many people find prolonged standing difficult: were it required in voluntary prayer, most would abandon it; the Lawgiver therefore tolerated omitting standing in it, to encourage its increase, just as He tolerated praying it on a mount while traveling (al-Mughni, 1/443; I'lam al-Muwaqqi'in, 1/303).

The evidence is his saying (peace and blessings of Allah be upon him):

The prayer of the one sitting is half the prayer of the one standing.

Sahih hadith: Ibn Majah (1230) and others

Al-Nawawi (may Allah have mercy on him) said: this hadith is understood of voluntary prayer performed sitting while able to stand: he then has half the reward of the one standing; but if he prays the nafl sitting due to his inability to stand, his reward is not diminished; rather it is equal to that of one standing (Sharh Muslim, 6/13). And Aisha (may Allah be pleased with her) reported: "The Messenger of Allah (peace and blessings of Allah be upon him) used to pray sitting and recite sitting; when there remained of his recitation the equivalent of 30 or 40 verses, he would stand and recite standing, then bow, then prostrate, then do the same in the second rak'ah" (Muslim, 731).

It is also reported, through another channel, the option of bowing and prostrating standing or sitting, the Messenger (peace and blessings of Allah be upon him) having done both: Aisha added that she never saw the Messenger of Allah (peace and blessings of Allah be upon him) pray the night prayer sitting until he grew old: he would recite sitting, and when he wished to bow he would stand, recite about 30 or 40 verses, then bow (al-Bukhari, 1097; Muslim, 731). And from her: "The Messenger of Allah (peace and blessings of Allah be upon him) would pray one night standing for a long time and one night sitting for a long time; when he recited standing he would bow and prostrate standing, and when he recited sitting he would bow and prostrate sitting" (Muslim, 730).

If he begins the voluntary prayer standing and then wishes to sit, or begins it sitting and then wishes to stand, this is permitted according to Abu Hanifah, by judicial preference (istishsan), and according to Malik, al-Shafi'i and Ahmad: for he is engaged in a voluntary act, free between standing and sitting at the start; the same applies after beginning, since he remains in a voluntary act; and the hadiths of Aisha mentioned above bear this out. Abu Yusuf and Muhammad of the Hanafis said that this is not permitted to him. Al-Kasani said: that is the analogy (qiyas), for beginning is binding, like a vow: if he vows to pray 2 rak'ahs standing, sitting is not permitted to him without an excuse; likewise if he begins standing.

To their saying that beginning is binding, it is answered: beginning is not binding by legal determination; it is binding only by necessity, in order to preserve from nullity what has become an act of worship; and what has become such remains worship through the persistence of the remaining substance of the prayer, not through the persistence of the remaining attribute: since voluntary prayer sitting is permitted in principle, realizing standing in what remains is not required. He is therefore not required to pray more than 2 rak'ahs, for what has been performed dispenses with addition, unlike the vow, which is the object of legal obligation: if he binds himself with the attribute, it becomes obligatory likewise (Bada'i' al-Sana'i', 1/297; Ma'ani al-Athar, 1/291; al-Bahr al-Ra'iq, 2/68; Durr al-Hukkam, 2/30; Umdat al-Qari, 7/205; Sharh Muslim, 6/11; Hilyat al-Ulama, 2/120; Kashshaf al-Qina', 1/441; Nayl al-Awtar, 3/101; al-Insaf, 2/188).

It is reported from Abu Hanifah that it is not permitted to pray the sunnah of Fajr or the Tarawih sitting, for each of them is a confirmed sunnah (Ibn Abidin, 2/14; al-Bahr al-Ra'iq, 2/98).