Fiqh al-Hadith: ➊ Salvation is dependent solely upon having faith in Allah and His Messenger, and acting upon the Qur’an and Hadith. Without Tawhid (monotheism) and Sunnah, there is nothing but darkness. Only the one who affirms Tawhid will enter Paradise. ➋ Before Tawhid, it is necessary to have knowledge of it, and then to affirm it with the heart, the tongue, and the body—this alone constitutes faith (iman).
Source: Adwa al-Masabih fi Tahqiq Mishkat al-Masabih, Page: 37
Hasan bin ur-Rabī’ narrated to us, Hammād bin Zayd narrated to us, on authority of Ayyūb and Hishām [bin Hassān], on authority of Muhammad [bin Sīrīn] ; and Fuḍayl [bin Īyāḍ] narrated to us on authority of Hishām [bin Hassān]; he said Mukhlad bin Husayn narrated to us, on authority of Hishām [bin Hassān], on authority of Muhammad bin Sīrīn , that he said: ‘Indeed this knowledge is faith, so carefully consider from whom you take your faith’.
Shaykh Maulana Abdul Aziz Alvi
Hadith Commentary:Benefits and Issues: Just as an animal cannot walk without legs, in the same way, a hadith cannot be accepted without a chain of transmission (isnad). If the question of the chain (isnad) did not exist, then every person would listen to something without investigation or verification and narrate it further, and that would become part of the religion. Thus, the protection and defense of the religion can be achieved through the chain of transmission (isnad); without it, the religion cannot be safeguarded from adulteration and innovations (bid‘ah).
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 26