Starting to recite Faatihah while rising from prostration
6-4-2016 | IslamWeb
Question:
What is the ruling on a person starting the recitation of the Faatihah before he is fully standing after the prostration. Is this something that nullifies the prayer?
Answer:
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.
Standing up straight while reciting Takbeerat Al-Ihraam (opening the prayer) and the Faatihah in the prayer is obligatory, as has been stated by the scholars. The Maaliki scholar Khaleel 
wrote, "The obligations of the prayer: Takbeerat Al-Ihraam while standing up straight for it ... reciting the Faatihah by moving one’s tongue while standing up straight for it..." [Mukhtasar Khaleel]
Haashiyat Ad-Dusooqi ʻala Ash-Sharh Al-Kabeer reads:
"His statement 'standing up straight for it' is linked with reciting the Faatihah for both the imaam and the one praying individually. It does not mean that standing up straight is an independent obligation in and of itself. This is the preponderant scholarly view in this regard. Based on this view, if the praying person cannot recite the Faatihah, then the obligation to stand up is waived. Another view suggests that standing up in prayer is an independent obligation and is not waived if the praying person is unable to recite the Faatihah. As for the one being led in the prayer, he is not obliged to stand up for reciting the Faatihah. If he leaned against a pillar during its recitation to such an extent that if the pillar were to be removed, he would fall, then his prayer is still valid..."
If the praying person recites the Faatihah while bowing, his prayer is not valid. Ad-Dardeer wrote, "If the praying person sat down or leaned against something while reciting the Faatihah, then his prayer is invalid. The same ruling applies if he leaned against something to such an extent that if it were to be removed, he would fall..." [Ash-Sharh As-Sagheer]
The Hanbali book Kashshaaf Al-Qinaaʻ reads, "When a (sick) person starts the prayer while unable to stand up straight but could do so during the prayer and recited only part of the Faatihah while standing up straight, then it is not sufficient for him, just like someone who is able to stand up straight but recited it while rising from (prostration)."
The scholarly view adopted by Islamweb is that it is obligatory on the person being led in the prayer to recite the Faatihah in each rakʻah (unit) of the prayer. Please, refer to fatwa 81333. Hence, whoever recites only part of the Faatihah in any rakʻah of the prayer while standing up straight, his prayer is invalid.
Allaah knows best.