Answered by Shaykh Faraz Rabbani
Is basmala considered a part of Fatiha by the hanafi jurists? if one, inadvertently leaves it out, is sajda sahw required?
This question was dealt with by Shaykh al-Islam Abu al-Su`ud in his masterly tafsir, Irshad al-`Aql al-Saleem (famous as ‘TafsirAbu al-Su`ud’), which many consider to be the greatest and most eloquent tafsir of the Qur’an and gave its author the title of ‘Khatib al-Mufassirin’.
(In the Name of Allah, Most Compassionate, Most Merciful) The imams differed concerning the basmala [‘Bimsillah al-Rahman al-Rahim’] at the beginning of the noble suras. Some said it is not from the Qur’an at all, this being the stand of Ibn Mas`ud (Allah be pleased with him), and the position of Malik, and the famous position of early Hanafi scholars, and upon it as the Qur’an reciters of Madina, Basra , and Sham. Others said that it is a single verse of the Qur’an that was revealed to separate [between suras] and to seek baraka [by beginning in the name of Allah], this being the correct position of the Hanafi school…” [1: 8]
Imam Zafar Ahmad Usmani explained, in hisAhkamal-Qur’an[1: 5-6]:
“(The Ruling of Saying The Basmala Before the Fatiha According to Abu Hanifa)
The transmission differed from Abu Hanifa (Allah have mercy on him) regarding this. According to the famous narration (zahir al-riwaya) , it is a confirmed sunna…
Fakhr al-Din al-Razi spoke at length on this issue, and presented sixteen arguments to prove that the basmala is a verse of the Fatiha. None of these arguments amount to much, however, because some of the arguments are easily answered and others do not negate our position, because the correct position of our school is that the basmala is a single, separate verse of the Qur’an, even though it is not from the Fatiha itself… And the author ofRuh al-Ma`ani [the great 19th Century tafsir in 30 volumes by Imam al-Alusi of Baghdad] answered every argument of Fakhr al-Din in detail, so whoever seeks a detailed answer should look there or in I`la’ al-Sunan [the 21-volume work on the hadith proofs of the Hanafi school, by the author].”
Therefore, given that the basmala is not necessary (wajib) but a confirmed sunna, one does not perform forgetfulness prostrations for leaving it out, because these are only required if one leaves a necessary (wajib) act. [Maraqi, Hashiya]
And Allah knows best.
 Zahir al-Riwaya (‘Famous narrations’) denotes the positions of our 3 imams (Abu Hanifa, Abu Yusuf, and Muhammad ibn al-Hasan) that were transmitted in the 6 most famous works of Imam Muhammad, all of which were made famous by the large number of students who transmitted them.