Foundations of the Sunnah & The Obligation of Adhering to The Sunnah and a Caution Against Innovation

Foundations of the Sunnah by Imaam Ahmed Ibn Hanbal

http://abdurrahman.org/sunnah/foundationsofsunnah.pdf

The Obligation of Adhering to The Sunnah and a Caution Against Innovation By Abdul-Azeez bin Baaz

http://s1.islamhouse.com/data/en/ih_books/signal/en_Obligation_of_Adhering_to_the_Sunnah.pdf