Some ḥadīth scholars have said that isnād is a synonym of sanad. 1 But others have rejected this synonymy outright and insist that these two terms are different. Isnād, according to them, is the ascription of a ḥadīth to the one who said it and is thus a means of attaining information about the chain of transmission, whereas the sanad it the chain of transmission itself. 2
The latter view is supported by a ḥadīth from Amīr al-Muʾminīn (‘a) where the term isnād has been used:
إِذَا حَدَّثْتُمْ بِحَدِيثٍ فَأَسْنِدُوهُ إِلَى الَّذِي حَدَّثَكُمْ فَإِنْ كَانَ حَقّاً فَلَكُمْ وَ إِنْ كَانَ كَذِباً فَعَلَيْهِ.
When you narrate a ḥadīth, ascribe it to the one who narrated it to you; for if it is true then you will gain [the reward] and if it is a lie, he will be responsible. 3
Based on this difference between isnād and sanad, those who define sanad as being information about the chain of transmission have erred 4 because this is the definition of isnād, not sanad. 5