The Effect of the Theory of Isnad Exchanging on "man la yaḥḍarahu al-Faqīh" and "tahdhīb al-aḥkām" and "al-Istibṣār"

Introduction
Two important sources for inferencing Islamic laws are the Qur'an and the Sunnah. The historical sensitivities to preserve and protect the Shia Narrative tradition have led to a large part of the Hadiths to be removed from the circle of reliable Hadiths. Therefore, addressing the Isnad problems of hadiths can be a serious development in this field. The theory of Isnad exchanging is one of these theories that it tries to open the way for trusting important hadiths by correcting some chain of transmitter of hadiths. The meaning of the theory of Isnad exchanging is to replace a part of the Isnad or the entire Isnad of a hadith that is weak due to being Majhul, Ḍaʻīf, Mursal or Munqaṭiʻ the Isnad. In this theory, by intromitting in the chain of transmitter of weak hadith and replacing that reliable part with that part, the Isnad problem of the hadith is solved.
Materials and Methods
By a descriptive-analytical method, this study presents the effect of the theory of Isnad exchanging in making the Isnads of some hadiths that Sheikh Ṣadūq narrative in Man lā Yaḥḍuruhu al-Faqīh, and Sheikh Ṫūsī in Tahdhīb al-ahkam and Al-Istibsār.
Results and Discussion
Emphasizing the conventional way of Isnad in books of hadith, that is not mentioning a part of the Isnad of hadith and completing the Isnad through listing all access path and chain of transmitter in end of book; and mention the different access path and chain of transmitter that they have had to their books; and and specifying to have all the books of Mashayekh or transmitters of the same class, this study argues that replacing and exchanging the Isnad can make Ḍaʻīf and Mursal Isnad, credible and correct one. Ayatullah Muslim Davari has explained and developed this new method that Ayatullah Khoui mentioned earlier. According to this method, reliable and valid Isnad replace weak and invalid one. The reason for the legality of such a exchanging of a chain of transmitter is the existence of a reliable and valid access path or access paths to all the books and hadiths of one of the reliable traditions that exists before the Majhul or Ḍaʻīf or … transmitter in the chain of hadith. In this study, evidence is provided that the collectors of al-Kutub al-ʾArbaʿah claim to have the reliable and valid access paths for all the books and narrated hadiths, and it is emphasized that in many cases that are explained in detail, since there are other authentic and valid access paths for them, if there was a weak path or chain to hadiths, those hadiths should still be considered authentic and valid. In fact, by accepting what has been said, that is owners of al-Kutub al-ʾArbaʿah have access to well-known al-Uṣūl and books of hadith, many existing chains of transmitter can be corrected using the theory of Isnad exchanging. This approach has been extended to Ayatullah Khoei and Davari; The existence of a common sheikh is considered sufficient to correct the weak access path of one transmitter through the reliable and valid access path of another transmitter; Because if their sheikh is one and the book is also one, and one of the two chain of transmitter and access path is sound, then the other chain of transmitter and access path is undoubtedly sound.
Conclusion
Then, if there were problems in one of the hadiths, such as one of the transmitters was Majhul or Ḍaʻīf, or a part of chain of transmitters was Mursal or Munqaṭiʻ, or such problems that make the hadith invalid, in this case, one can rely on the theory of Isnad exchanging; A theory that gives credibility to the hadith By changing the hadith Isnad and removing the invalid part and replacing it with a correct, reliable and valid one.