1: The Sunnah is Islaam and Islaam is the Sunnah
Imaam al-Barbahaari (rahimahullaah) said:

All praise is for Allaah who guided us to Islaam and blessed us with it and placed us in the best nation, so we ask Him to grant us that we keep to that which He loves and is pleased with and avoid that which He hates and which angers Him.

Know that Islam is the Sunnah, and the Sunnah is Islaam[1] and one of them cannot be established without the other.

NOTES
1. The Prophet said, "He who turns away from my Sunnah is not from me." Reported by al-Bukhaaree (Eng. trans. 7/1-2/no.l), Muslim (Eng. Trans. 2/703/n0.3236) and an-Nasaa'ee.

Abu Hurairah said that Allaah's Messenger said, "All of my Ummah will enter Paradise except those who refuse." It was said, "Who will refuse?" He replied. "Whoever obeys me enters Paradise and whoever disobeys me has refused." Reported by al-Bukhaaree (Eng. trans. 9/284/n0.384).

Imaam az-Zuhree (the famous taabi'ee, d.124H) said,"The people of knowledge who came before us used to say,'Salvation lies in clinging to the Sunnah.'" Reported by ad-Daarimee in his Sunan (no.96).

Imaam Maalik said,"The Sunnah is like the Ark of Noah. Whoever embarks upon it reaches salvation and whoever refuses is drowned." Quoted by Shaikh ul-Islaam Ibn Taimiyyah in Majmoo' ul-fataawaa (4/57).