Amongst the countless blessings which Almighty ALLAH has bestowed upon the Muslims is that He has preserved their religion for them and provided the appropriate means for Islam to be safeguarded and preserved, in that He has raised erudite scholars through whom the Sunnah of the Noble Prophet, Muhammad ibn Abdullaah صلّی الله علیهِ وآلهِ وسلم, the seal of the prophets صلّی الله علیهِ وآلهِ وسلم, has been preserved. Thus the Book of Allah and the Sunnah of the Prophet صلّی الله علیهِ وآلهِ وسلم provide evidence against mankind. One of the scholars through whom Allah preserved the Sunnah was Imaam Ahmad ibn Hanbal (Rahimahullah), and one of the books that he wrote to preserve the Sunnah is al-Musnad, which is one of the major collections of the noble Sunnah.
Muslim scholars, particularly hadeeth scholars, were keen on ahaadeeth with few narrators between the hadeeth reporter and the Prophet صلّی الله علیهِ وآلهِ وسلم. In fact, Imaam Ahmad reported more than three hundred "thulaathiyyaat", ahaadeeth with only three narrators between him and the Prophet صلّی الله علیهِ وآلهِ وسلم. These ahaadeeth were collected from al-Musnad by Shaikh Muhammad ibn Ahmad ibn Saalim as-Saffaareenee al-Hanbalee (Rahimahullah) in a separate book.
This example clearly points to the great care shown by hadeeth scholar to the Prophet's Sunnah, as they were keen to compile the Sunnah with the soundest chains of narrators (isnaad) and convey it in the easiest manner possible, from leading scholars of hadeeth who were of extremely good character and who approached the reports with accuracy and deep knowledge, in compliance with to the Prophet's instructions: "Convey [whatever you learn] from me. even if it is just one verse." (Narrated by al-Bukhaaree)