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, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.
It is known that standing up is a pillar of the prayer when reciting Takbeerat Al-Ihraam (opening takbeer) and the Faatihah. An-Nawawi said, “The praying person should recite takbeer while standing...” [ʻUmdat At-Taalibeen]
The author of Al-Fawaakih Ad-Dawaani said, “You should know that the obligations of the prayer are seventeen: intention, Takbeerat Al-Ihraam, standing up for it (Takbeerat Al-Ihraam), reciting the Faatihah, standing up for it (the Faatihah), bowing, and standing up for it ...”
The scholars stated that if the person is unable to stand up while reciting the Faatihah, then he recites Takbeerat Al-Ihraam while standing up and then sits down when reciting the Faatihah. Haashiyat Ad-Dusooqi ʻala Ash-Sharh Al-Kabeer reads, “If he is unable to recite the Faatihah while standing up, he sits down. The same view was adopted by Ibn Al-Haajib. Ibn Farhoon said, ‘The apparent indication of the statement suggests that the obligation of standing up is waived even while reciting Takbeerat Al-Ihraam; but this is not so; he should stand up while reciting Takbeerat Al-Ihraam and then sit down to recite the Faatihah and then stand up again to perform rukooʻ (bowing)...”
Al-Hattaab said, “If he is able to stand up for some time, then he should stand up, whether it is for reciting Takbeerat Al-Ihraam only or more because standing up is required while reciting the Quran in the prayer. So if he is unable to stand up while reciting the whole chapter, then he should recite whatever he can of it while standing up and then sit down, and the obligation of standing up while reciting the rest is waived...” [Mawaahib Al-Jaleel]
Al-Kharashi said, “If the praying person could not recite the whole Faatihah or part of it while standing up and can do so while sitting down, then he should sit down and recite it after reciting Takbeerat Al-Ihraam while standing up and recite whatever he can of the Faatihah and complete the rest of it while sitting down...” [Sharh Mukhtasar Khaleel]
Hence, dear Brother, the obligation of standing up is not entirely waived even for reciting the Faatihah if the person is able to recite part of it while standing up. If he can stand up, then he should stand up while reciting whatever he is able to recite of the Faatihah and then sit down. There is another scholarly view that holds that the obligation of standing up is waived in its totality. Al-ʻAdawi said, “If he is unable to stand up while reciting part of the Faatihah, then there are two scholarly views as to whether the obligation of standing up is waived or not. One view suggests that he should recite the whole Faatihah while sitting down, and the second view suggests that he should recite whatever he can of the Faatihah while standing up and then sit down; the second opinion is the more famous one...” [Haashiyat Al-ʻAdawi]
Allaah knows best.