Continuation of the previous discussion on the evidentiary value of the mursal hadith.

The Shaykh : ... because all the Companions are trustworthy. For this reason—namely, that all the Companions are trustworthy—scholars of hadith accept as evidence the statement of a Tabi'i: "A man from among the Companions of the Prophet (peace and blessings be upon him) told me." This man is unknown, but because he was described as being from among the Companions of the Prophet (peace and blessings be upon him), the anonymity did not harm the report; for all the Companions of the Prophet (peace and blessings be upon him) are trustworthy. If the definition of mursal in the Bayquniyyah had been: "That from which the Companion is dropped," this would not have been the case...; for in that case, it would be like the statement of that Tabi'i: "A man from among the Companions of the Prophet (peace and blessings be upon him) told me." However, the use of the mursal hadith as evidence was rejected due to the possibility that the Tabi'i took it from someone other than a Companion, from a Tabi'i like him, from a Companion, from the Messenger of Allah.
Al-Hafiz Ibn Hajar—may Allah have mercy on him, who is an imam in this subject—mentions that it has become established for us, through induction, that in some hadiths—and peace be upon you—there are four Tabi'ins between the Tabi'i and the Companion; that is: a Tabi'i from a Tabi'i from a Tabi'i from a Tabi'i from a Tabi'i from a Companion. Who can know... about these people? So if it is assumed to be a Tabi'i from a Tabi'i from a Companion, then this Tabi'i who is between the Companion and the Tabi'i... is unknown. For this reason, scholars of hadith inclined toward not using the mursal hadith as evidence.
Al-Hafiz Ibn Hibban also mentioned, on this occasion, a benefit in refuting those who held that the mursal hadith is to be used as evidence; for their argument is to assume the best of the mursal narrator; that is, those who argue for the mursal hadith say that if the mursal narrator is trustworthy, then his omission of the intermediary between him and the Companion means that he trusts that intermediary which he dropped. And for this reason, we use the mursal hadith as evidence. Some of them even exaggerated and said: "Whoever sends [a hadith] has spared you the path of research!" As for whoever connects [the chain], you must look into the man from whom he heard it. Al-Hafiz Ibn Hibban refuted these people with a beautiful and very strong scientific method; he said: "If such an argument were valid, the value of the isnad would be invalidated." How? He said: If we use the mursal hadith as evidence based on our good opinion of the mursal narrator, then let us also have a good opinion of the mu'dal; that is, the one who dropped two intermediaries, namely: a Tabi'i from a Tabi'i. He says: "A man from among the Tabi'ins told me from Abu Hurayrah—for example—from the Messenger of Allah." And so we continue this way to our present time. If a scholar says: "The Messenger of Allah (peace and blessings be upon him) said," we trust his statement and take his hadith. This invalidates the value of the isnad. And among the characteristics of this Ummah is that Allah (Mighty and Majestic) distinguished it from all other nations by inspiring it with the knowledge of isnad. This is a fact that the disbelieving Orientalists today acknowledge; that the Islamic Ummah brought forth a knowledge that nations did not know, neither before nor after, which is the isnad.
Some scholars of the Salaf, such as 'Abdullah ibn al-Mubarak, elevated the status of the isnad, where he used to say: "The isnad is part of the religion, and were it not for the isnad, whoever wished would say whatever he wished." And this is a fact. Using the mursal hadith as evidence contradicts the value of this isnad which Ibn al-Mubarak (may Allah have mercy on him)—as you have heard—elevated. So the original ruling regarding the mursal hadith is that it is not used as evidence, but it is treated like any other weak hadith that is not severely weak. This is what Imam al-Shafi'i (may Allah have mercy on him) held, where he said: "If a hadith comes mursal from one route and connected from another route—even if with a chain that has weakness—then the mursal hadith is thereby strengthened by this connected hadith, even if its chain is weak with a weakness that is not severe; so one of them then strengthens the other." And the more routes there are for the mursal hadith, the stronger it becomes.
Finally: What confirms what the majority of scholars of hadith held regarding not using the mursal hadith—as well as the munqati' hadith—as evidence is that we found some Tabi'ins narrating a hadith from one of the Companions, and this Tabi'i is known for tadlis; such as al-Hasan al-Basri. And yet, when he issues a ruling in the issue in which he narrated the marfu' hadith, he rules contrary to his hadith. So if the hadith he narrated from the Companion is true, al-Hasan, despite his high status, is a mudallis; that is, he used to narrate from the Companion what he did not hear from him. There was an intermediary between him and the Companion whom he did not mention. And yet he narrated the hadith from that Companion. Then, when the time came to answer a question or explain a verse, he explained the verse contrary to the hadith he had narrated from the Companion. So this is an action by the mursal narrator himself that indicates to us that he did not consider what he sent [mursal]; that is, he did not name the intermediary between him and the Companion.
This is what can be said regarding the mursal hadith.