It may surprise some people to learn that one example often cited in hadith textbooks of such a hidden flaw (‘illa) is from Sahih Muslim, all of whose hadiths are rigorously authenticated (sahih), as Ibn al-Salah has said, "except for a very small number of words, which hadith masters of textual evaluation (naqd) such as Daraqutni and others have critiqued, and which are known to scholars of this level" (‘Ulum al-hadith). The hadith of the present example was related by Muslim from the Companion Anas ibn Malik in several versions, which might convince those unaware of its flaw to believe that someone at prayer should omit the Basmala or "Bismi Llahi r-Rahmani r-Rahim" at the beginning of the Fatiha. According to the hadith, Anas ibn Malik (Allah be well pleased with him) said, 

I prayed with the Messenger of Allah (Allah bless him and give him peace), Abu Bakr, ‘Umar, and ‘Uthman, and they opened with "al-Hamdu li Llahi Rabbi l-‘Alamin,"not mentioning "Bismi Llahi r-Rahmani r-Rahim" at the first of the recital or the last of it [and in another version, "I didn’t hear any of them recite ‘Bismi Llahi r-Rahmani r-Rahim’"] (Muslim, 1.299).

Scholars say the hadith’s flaw lies in the negation of the Basmala at the end, which is not the words of Anas, but rather one of the subnarrators explaining what he thought Anas meant. Ibn al-Salah says: "Its subnarrator related it with the above-mentioned wording in accordance with his own understanding of it" (Muqaddima Ibn al-Salah (b01), 99). This hadith is given as an example of a "hidden flaw" in a number of manuals of hadith terminology such as hadith master (hafiz) Suyuti’s Tadrib al-rawi (1.254–57); hadith master Ibn al-Salah’s Ulum al-hadith; hadith master Zayn al-Din al-‘Iraqi’s al-Taqyid wa al-idah (98–103); and others. Al-‘Iraqi says, "A number of hadith masters (huffaz) have judged it to be flawed, including Shafi‘i, Daraqutni, Bayhaqi, and Ibn ‘Abd al-Barr" (ibid., 98). 

Now, Bukhari has related the hadith up to the words "and they opened with ‘al-Hamdu li Llahi Rabbi l-‘Alamin’"; without mentioning omitting the Basmala (Bukhari, 1.189), and Tirmidhi and Abu Dawud relate no other version. Scholars point out, in this connection, that the words "al-Hamdu li Llahi Rabbi l-‘Alamin" were in fact the name of the Fatiha, for the Prophet (Allah bless him and give him peace) and his Companions often used the opening words of suras as names for them; for example, in the hadith in Sahih al-Bukhari of Abu Sa‘id ibn al-Mu‘alla, who relates that the Prophet (Allah bless him and give him peace) said: 

"I will teach you a sura that is the greatest sura of the Qur’an before you leave the mosque." Then he took my hand, and when he was going out, I said to him, "Didn’t you say, ‘I will teach you a sura that is the greatest sura of the Qur’an before you leave the mosque’?" And he said: "‘Al-Hamdu li Llahi Rabbi l-‘Alamin’: it is the Seven Oft-Recited [Verses] (al-Sab‘ al-Mathani) and the Tremendous Recital (al-Qur’an al-‘Adhim) that I have been given" (ibid., 6.20–21).

In this hadith, "Al-Hamdu li Llahi Rabbi l-‘Alamin" is plainly the name of the Fatiha, and means nothing besides, for otherwise, it is one verse, not seven. ‘A'isha, who was one of the ulama of the Sahaba, also referred to names of suras in this way, as in the hadith of Bukhari that

the Prophet (Allah bless him and give him peace), when he went to bed each night, joined his hands together, blew a light spray of saliva upon them, and read over them "Qul huwa Llahu Ahad," "Qul a‘udhu bi Rabbi l-Falaq," and "Qul a‘udhu bi Rabbi n-Nas"; then wiped every part of his body he could with them (ibid., 233–34),

which clearly shows that she named the suras by their opening words (after the Basmala), as did other early Muslims (such as Bukhari in his chapter headings in the section of his Sahih on the Virtues of the Qur’an, for example). So there is no indication, in the portion of the Anas hadith’s wording that is agreed upon by both Bukhari and Muslim; namely, "I prayed with the Messenger of Allah (Allah bless him and give him peace), Abu Bakr, ‘Umar, and ‘Uthman, and they opened with ‘al-Hamdu li Llahi Rabbi l-‘Alamin,’" that the Basmala was not recited aloud. Says Tirmidhi: "Imam Shafi‘i has said, ‘Its meaning is that they used to begin with the Fatiha before the sura, not that they did not recite "Bismi Llahi r-Rahmani r-Rahim."’ And Shafi‘i held that the prayer was begun with ‘Bismi Llahi r-Rahmani r-Rahim,’ and that it was recited aloud in prayers recited aloud" (Tirmidhi, 2.16).

Hadith scholars who are masters of textual critique, like Daraqutni and others, consider the words of the Anas hadith"not mentioning ‘Bismi Llahi r-Rahmani r-Rahim,’" which outwardly seem to suggest omitting the Basmala, to be vitiated by an ‘illa or "hidden flaw" for many reasons, a few of which are:

—It is established by numerous intersubstantiative channels of transmission (tawatur), that the Prophet (Allah bless him and give him peace) said, "There is no prayer for whoever does not recite the Fatiha" (Bukhari, 1.192). That the Basmala is the Fatiha’s first verse is shown by several facts: 

First, the Sahaba affirmed nothing in the collation of the Qur’an (mushaf) of ‘Uthman’s time except what was Qur’an, and they unanimously placed the Basmala at the beginning of every sura except surat al-Tawba. 

Second, the Prophet (Allah bless him and give him peace) said, "When you recite ‘al-Hamdu li Llah,’ recite ‘Bismi Llahi r-Rahmani r-Rahim,’ for it is the Sum of the Qur’an (Umm al-Qur’an), and the Compriser of the Scripture (Umm al-Kitab), and the Seven Oft-Repeated [Verses] (al-Sab‘ al-Mathani)—and ‘Bismi Llahi r-Rahmani r-Rahim’ is one of its verses" (Bayhaqi, 2.45; and Daraqutni, 1.312), a hadith related with a rigorously authenticated (sahih) channel of transmission to the Prophet (Allah bless him and give him peace), and through another chain to Abu Hurayra alone (Allah be well pleased with him). 

Third, Umm Salama relates: "The Prophet (Allah bless him and give him peace) used to recite: ‘Bismi Llahi r-Rahmani r-Rahim. al-Hamdu li Llahi Rabbi l-‘Alamin,’ separating each phrase"; a hadith which Hakim said was rigorously authenticated (sahih) according to the conditions of Bukhari and Muslim, which Imam Dhahabi corroborated (al-Mustadrak, 1.232). Daraqutni also relates from Umm Salama that "the Prophet (Allah bless him and give him peace) when he used to recite the Qur’an would pause in his recital verse by verse: ‘Bismi Llahi r-Rahmani r-Rahim: al-Hamdu li Llahi Rabbi l-‘Alamin: ar-Rahmani r-Rahim: Maliki yawmi d-din.’" Daraqutni said, "Its ascription is rigorously authenticated (sahih); all of its narrators are reliable" (Daraqutni, 1.312–13). These hadiths show that the Basmala was recited aloud by the Prophet (Allah bless him and give him peace) as part of the Fatiha.

Fourth, Bukhari relates in his Sahih that when Anas was asked how the Prophet (Allah bless him and give him peace) used to recite, "he answered: ‘By prolonging [the vowels]’—and then he [Anas] recited ‘Bismi Llahi r-Rahmani r-Rahim,’ prolonging the Bismi Llah, prolonging the r-Rahman, and prolonging the r-Rahim" (Bukhari, 6.241), indicating that Anas regarded this as part of the Prophet’s Qur’an recital and that the Prophet (Allah bless him and give him peace) recited it aloud. 

Fifth, Daraqutni has recorded two hadiths, both from Ibn ‘Abbas, and has said about each of them, "This is a rigorously authenticated (sahih) chain of transmission, there is not a weak narrator in it," of which the first is: "The Prophet (Allah bless him and give him peace) used to recite ‘Bismi Llahi r-Rahmani r-Rahim,’ aloud"; and the second is: "The Prophet (Allah bless him and give him peace) used to begin the prayer with ‘Bismi Llahi r-Rahmani r-Rahim’" (al-Nawawi: al-Majmu‘, 3.347). 

—Imam al-Mawardi summarizes: "Because it is established that it is obligatory to recite the Fatiha in the prayer, and that the Basmala is part of it, the ruling for reciting the Basmala aloud or to oneself must be the same as that of reciting the Fatiha aloud or to oneself" (al-Hawi al-kabir, 2.139).

—Imam Nawawi says: "Concerning reciting ‘Bismi Llahi r-Rahmani r-Rahim’ aloud, we have mentioned that our position is that it is praiseworthy to do so. Wherever one recites the Fatiha and sura aloud, the ruling for reciting the Basmala aloud is the same as reciting the rest of the Fatiha and sura aloud. This is the position of the majority of the ulama of the Sahaba and those who were taught by them (Tabi‘in) and those after them. As for the Sahaba who held the Basmala is recited aloud at prayer, the hadith master (hafiz) Abu Bakr al-Khatib reports that they included Abu Bakr, ‘Umar, ‘Uthman, ‘Ali, ‘Ammar ibn Yasir, Ubayy ibn Ka‘b, Ibn ‘Umar, Ibn ‘Abbas, Abu Qatada, Abu Sa‘id, Qays ibn Malik, Abu Hurayra, ‘Abdullah ibn Abi Awfa, Shaddad ibn Aws, ‘Abdullah ibn Ja‘far, Husayn ibn ‘Ali, Mu‘awiya, and the congregation of Emigrants (Muhajirin) and Helpers (Ansar) who were present with Mu‘awiya when he prayed in Medina but did not say the Basmala aloud, and they censured him, so he returned to saying it aloud" (al-Majmu‘, 3.341). 

These are some reasons why scholars regard the Anas hadith in Sahih Muslim to be mu‘all or "flawed." We cannot here discuss other aspects of the hadith such as the flaws in its chain of narrators, which are explained in detail in Zayn al-Din ‘Iraqi’s al-Taqyid wa al-idah (100–101), though the foregoing may give a general idea why it has been considered flawed by hadith masters (huffaz) such as Suyuti, ‘Iraqi, Ibn Salah, Ibn ‘Abd al-Barr, Daraqutni, and Bayhaqi—and why the shari‘a ruling apparently deducible from the end of the hadith; namely, omitting the Basmala when reciting the Fatiha at prayer, has been rejected by al-Shafi‘i, Nawawi, and others, who hold that the Basmala is recited aloud whenever the Fatiha is. (The position of Abu Hanifa and Ahmad ibn Hanbal, it may be noted, is that one recites the Basmala to oneself before the Fatiha, thus joining between hadiths on both sides by interpreting the "omitting" in the Anas hadith in other than its apparent sense, to mean merely "reciting to oneself.") In any case, it is clearly not a story of "the hadith in Sahih Muslim that the Imams didn’t know about," as some of the unlearned seriously suggest today, but rather a difference of opinion in hadith authentication involving the highest levels of shari‘a scholarship.