How important is it to memorise the isnads (chains of narration) of hadiths?
Question

Is it essential to memorise chains of narrations in the order of their hadiths, or is it sufficient to remember the names of the narrators?
What is the benefit of memorising the chains of narrations as they are?
Praise be to Allah.The importance of the isnad (chain of narration) in determining which reports are sound and distinguishing them from those which are weak or false is well known.
Al-Hakim (may Allah have mercy on him) said:
Were it not for the isnads and the hadith scholars seeking out the isnad for every hadith, and their extreme care in memorizing and preserving the isnads, the teachings of Islam would have been lost and the heretics and innovators would have been able to fabricate hadiths and tamper with the isnads. If the reports did not have isnads, they would be of no benefit."(Ma‘rifat ‘Ulum al-Hadith  p. 115).
Al-Qadi ‘Iyad (may Allah have mercy on him) said:
You should understand, first of all, that the basis of the hadith is the isnad; through it the soundness of the hadith can be proven and it can be established whether the isnad is uninterrupted."(Al-Ilma‘  p. 267).
Thus it becomes clear that learning the chains of narration through which the hadith texts were narrated, and studying them, is not essential for everyone. Rather it is required of the one who wants to learn the science of hadith and specialize in it, so that he can acquire the ability to distinguish between hadith reports and determine which are sound and which are weak. Such a person must pay attention to learning the isnads, either by memorizing them or constantly referring to the books of hadith in which the isnads are shown and researching the narrators of each hadith, until he develops skills and acquires knowledge of the narrators of hadith. The one who is ignorant about the narrators and lacks the skills to critique hadiths cannot be a scholar of hadith, no matter how much he memorizes of the texts.
Shaykh ‘Abd ar-Rahman al-Mu‘allimi (may Allah have mercy on him) said:
A man cannot be called a scholar until he acquires knowledge and information about the narrators of hadith. In Tadrib ar-Rawi it says: Ar-Rafa‘i and others said: When the word scholar is mentioned, that will exclude those who hear the hadith but have no knowledge of the chains of narrators or the names of narrators.
Az-Zarqani said: As for the scholars, in their view the title of hadith scholar (muhaddith) cannot be given to anyone except one who has memorized the texts of the hadith and knows the character of the narrators and is able to critique them.
At-Taj as-Subki said: … The hadith scholar is the one who knows the isnads and how to critique them, and knows the names of the narrators.
It was narrated from al-Mizzi that he was asked about who deserves to be called a hadith scholar, and he said: At a minimum, the number of narrators whom he knows, along with their biographies, circumstances and countries where they lived should be greater than the number of those whom he does not know, so that he can evaluate the hadith.
So the scholar needs to know the circumstances of those narrators who are his contemporaries, either by finding out about them directly or finding out about them from what trustworthy scholars have said about them. And he needs to learn about the character and circumstances of those narrators who came before him from what trustworthy scholars said about them, or from what trustworthy scholars narrated from other trustworthy scholars, and so on. And he must memorize all of that as he must memorize the hadith and its isnads. Thus some of them memorized thousands of hadiths, some of them memorized tens of thousands, and some of them memorized hundreds of thousands, along with their isnads.
End quote from Muhadarah fi ‘Ilm ar-Rijal wa Ahammiyatuhu – in Athar al-Mu‘allimi (15/227).
Undoubtedly, memorizing the isnads of hadiths as they appear in the books of hadith is better and more appropriate than memorizing the names on their own. That is for many reasons, the most important of which are:
1.. Memorizing the hadith with its isnad, as it was narrated, helps one to remember the status of this hadith and whether it is sound or weak.
2.. The one who memorizes the isnads as they are will acquire knowledge of the different levels or generations of the narrators, so he will learn about the shaykhs and students of each narrator. Learning about the levels or generations of the narrators is important, as is well known among specialists in this field, and it can solve many issues.
Al-‘Iraqi (may Allah have mercy on him) said:
It is important to learn about the levels and generations of narrators, because there may be two narrators with identical names, and one may think that only one person is referred to. But you can distinguish between them when you know the level or generation to which each of them belong, if they are of different levels. If they belonged to the same level or generation, the matter may be confusing, but knowing the shaykhs from whom they narrated or the students to whom they narrated will help one to differentiate between them. One of the two who have identical names may not have narrated from the same shaykhs as the other. But if they had the same shaykhs and the same students, in that case the matter is more confusing, and only people of knowledge could differentiate between them.
Because they lacked knowledge of the levels and generations of narrators, some scholars made mistakes and thought that a narrator was someone else, or they may have regarded a narrator as belonging to the wrong level or generation."(Sharh at-Tabsirah wa’t-Tadhkirah 2/342-343).
3.. Isnads should be memorised with the wording in which each narrator received the hadith and transmitted it to his students; and whether there was a clear statement such as “I heard” or “he narrated to us” or “he told us”, or that was not stated clearly and the report simply says “it was narrated from” and so on. All of this will enable the scholar to acquire the skill to differentiate between uninterrupted and interrupted isnads.
Conclusion:
Memorizing the names of the narrators along with the chains of narration is the methodology that was adopted by the hadith scholars of the early generations and those who came after them, and it has proven to be very useful. The wise person will make the most of his time by following the method of learning and seeking knowledge which has been tried and tested.
But this is only required for specialists in this field and those who aspire to attain the pinnacle of this branch of knowledge. As for ordinary people, it is sufficient for them to memorize whatever they are able to of the texts – the words of the Prophet (blessings and peace of Allah be upon him) – and to study those words and understand them.
And Allah knows best.