Scholars of Islamic Law differentiate between two types of Prophetic actions and sayings: actions and sayings that are meant to be part of the Shari`ah (Islamic way and rules for life) and others that are only part of the Prophet's life as a human, which are not always meant to be a law for every Muslim to follow.
The Mosque of the Prophet Muhammad at Madinah in modern-day Saudi Arabia.
They call these two kinds of Prophetic tradition as-sunnah at-tashri`yyah (legislative Tradition) and as-sunnah ghair at-tashri`yyah (non-legislative tradition). For example, one of the Prophet's Companions, Talha, narrated the following:
I was walking with the Prophet(peace and blessings be upon him) when he passed by some people at the tops of their palm trees. He asked, "What are they doing?" They answered, "Pollinating the male into the female." He replied, "I do not think that this will be of benefit." When they were told about what the Prophet said, they stopped what they were doing. Later, when the trees shed their fruits prematurely, the Prophet was told about that. He said, "If it is good for them they should do it. I was just speculating. So pardon me. But if I tell you something about God, then take it because I would never lie about God." Another narrator said that the Prophet (peace and blessings be upon him) added, "You know your worldly affairs better than I." (Muslim)
This hadith shows one such non-legislative judgment given by the Prophet (peace and blessings be upon him), which he made to the best of his knowledge. The hadith even shows an error in this technical advice, which the Prophet and his Companions discovered later via human experience, rather than via divine revelation.
The rationale behind this hadith may be to show that it is not part of the Prophet's mission to contribute to technology and other similar worldly affairs through the revelation. Rather, human empirical experience is meant to be the only means for these developments.
Regarding the error that happened concerning the palm trees, the word `ismah (protection) is mentioned in the Qur'an in the context of the Prophet being protected from people's whims and Satan's delusions. The protection of all prophets in the above sense is an Islamic belief, which is a precondition to trusting the prophets' message and following their example. However, the Islamic definition of infallibility does not necessarily include technical worldly matters that are not part of conveying the message, as the above example shows.
Not for Every Muslim
Furthermore, if the tradition or hadith is of the legislative type, it is not always necessarily and literally meant for all Muslims. Some rulings are for rulers only, some are for judges only, and so on. The following is one example:
Hind bint `Utbah complained to the Prophet (peace and blessings be upon him) about the greediness of Abu Sufyan (her husband) and asked whether she was allowed to take from his money without his knowledge. So the Prophet said, "Take what you and your children normally need (without telling Abu Sufyan)." (Al-Bukhari)
Scholars commented on this hadith that the Prophet was acting here as a judge rather than a prophet. In other words, he allowed Hind in her specific case to do that, but the hadith does not give every woman a right to take whatever she wants from her husband's money without his knowledge, just for her own whim. Scholars maintain that this hadith is for judges to learn from when they make a similar judgment, but not for every Muslim.
The Margin of Error
It is true that there is a chance of error in this process. That is why scholars differentiated between different levels of authenticity, concerning the discipline of knowledge of Prophetic Hadith, by setting precise and rigid criteria. The following are two of these levels —among others— that are relavant here:
1. Mutawatir (recurring, most famous). These are narrations that are conveyed through a large number of people who could not possibly agree to lie.
The Qur'an and a certain number of Prophetic traditions fall under this category. The Qur'an, for example, was recited by thousands of people, and their recitations are the same. It is a logical conclusion that one can build firm beliefs and true obligations on this level of authenticity.
2. Ahad (individual, single-chained narrations). These are narrations according to one or two narrators, and hence are less "confirmed" than the first kind.
Scholars judged that these kinds of narrations could teach us about halal (lawful) and haram (forbidden), but could not be evidence of faith in their own right. This is because of the possibility of error in something that is narrated by only one or two people.
But a possibility of error in Companions' narrations should not discredit them completely. There are levels of authenticity and there are many sources of error that do not necessarily discredit a person. So if the person is trustworthy, Muslims accept the person's account but do not build matters of faith on it unless it is confirmed by a number of other narrators or witnesses.
In addition, scholars reject many hadiths because they are not up to the level of authenticity that implies any credibility. One example is when the narrator is known to be forgetful, ill-intentioned, or biased one way or another. That is why it is important to check the authenticity of a hadith before taking it, especially in matters related to Islamic creed and jurisprudence.
Muslim scholars have also set specific criteria for narrators of hadith before they can be accepted as narrators. These criteria are related to the biography of the narrator, including his or her reputation and moral attitude. Hadith authenticity is an independent discipline of knowledge in itself.