Assalaamu alaykum Shaykh. According to the Ahnaf Qirat, it is only obligatory in the first two Rak‘ahs (units of prayer) of the obligatory prayer, and according to them, then even if u remain silent in the second two Rak‘ahs of the obligatory prayer, your prayer is fine. I wonder if you could please give us a brief answer; where did they get it from, and what is the proof for this? May Allaah reward you.

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger. 

According to the Hanafis, it is better to recite the Faatihah in the last two Rak‘ahs of the obligatory prayer. However, if the worshiper remains silent and does not recite it, then he committed a mistake but his prayer is valid. Another view holds that he has not committed a mistake because it is authentically established, according to Hanafis, that the worshiper is given the choice to recite the Faatihah or remain silent in the last two Rak‘ahs of the obligatory prayer. The Hanafi scholar Al-Haskafi wrote:

“Reciting the Faatihah in the third and fourth Rak‘ahs of the prayer is an act of the Sunnah according to the most trusted view in the Hanafi school. There is no harm if he recited more (of the Quran), and he is given the choice either to recite the Faatihah - Al-‘Ayni underlined that the correct view is that it is obligatory to recite the Faatihah (in the third and fourth Rak‘ahs) - or recite Tasbeeh (saying: subaanallaah [glory be to Allah]) thrice, or remain silent for the same amount of time. It is said in An-Nihaayah that the worshiper may remain silent for the time of saying subhaanallaah once. If he remained silent, he has not committed a mistake according to the view of the Hanafi school, because it has been reported on the authority of ‘Ali and Ibn Mas‘ood that the person has the choice (either to recite the Faatihah, recite Tasbeeh, or remain silent). This is the reason for interpreting the reported observation of reciting the Faatihah as not to necessarily indicate that it is obligatory.” [Ad-Durr Al-Mukhtaar]

Ibn ‘Aabideen wrote:

“The Hanafis unanimously agreed in Thaahir Ar-Riwaayah (i.e. the view reported on the authority of Muhammad ibn al-Hasan through trustworthy transmitters from Imaam Abu Haneefah) that it is better for the praying person to recite the Faatihah. However, if he settled for reciting Tasbeeh instead, he bears no sin for it. If he remained silent, it has been stated in Al-Muheet that this is a mistake because it is prescribed for the praying person to recite the Quran in the prayer to celebrate the remembrance of Allah and praise Him. This is why it is enjoined to recite the Faatihah because it is all about glorifying and praising Allah. If the praying person deliberately remains silent in the last two Rak‘ahs, he has done wrong for neglecting the act of the Sunnah. If he forgetfully remains silent, he is not liable for Sujood as-Sahw (prostration of forgetfulness). Other scholars underlined that the praying person, according to Thaahir Ar-Riwaayah, has the choice either to recite the Faatihah, or Tasbeeh, or remain silent, and that remaining silent is not wrong ... The author of Al-Badaa'i` said, 'The most likely correct view is the answer stated in Thaahir Ar-Riwaayah since it has been narrated on the authority of ‘Ali and Ibn Mas‘ood, may Allah be pleased with them, that they held that the praying person has the choice in the last two Rak‘ahs; he may recite (Al-Faatihah), and he may remain silent, and he may recite Tasbeeh. This matter cannot be decided by Qiyaas (analogy), as what was reported on their authority is like what was reported on the authority of the Prophet, sallallahu ‘alayhi wa sallam.'” [Radd Al-Muhtaar `ala Ad-Durr Al-Mukhtaar]

Allah knows best.