• In obligatory prayers, standing is obligatory, because Allāh, Exalted is He, says, “And stand before Allāh, devoutly obedient.” The Prophet (May Allāh praise him and Peace be upon him) also said to ‘Imrān Ibn Ḥuṣayn, “Pray standing; and if you cannot, pray sitting; and if you cannot, pray on your side” [Reported by Imam Bukhārī 1117].

So, if somebody does not stand, and that is due to a legitimate excuse, such as illness or fear, he is excused and prays according to his circumstances, whether sitting or on his side.

• In optional prayers, it is sunnah (preferred) to stand, but it is not a pillar. However, there is greater virtue in praying standing than in praying sitting, because the Prophet (May Allāh praise him and Peace be upon him) said, “If you pray sitting, you will get half of the reward of somebody who prays standing” [Reported by Imam Muslim: 735].