Sunnah describes everything that the Prophet Mohammed (peace be uon him) said, did or implied. A believer has faith in the Quran & the Sunnah.
The Muslims are agreed that the Sunnah of the Prophet Muhammad (may Allah bless him and grant him peace) is the second of the two revealed fundamental sources of Islam, after the Glorious Qur'an. The authentic Sunnah is contained within the vast body of Hadith literature.
Some of the Hadith (sayings
of the Prophet) are:
Our Prophet (peace be upon him) said that Allah thus stated: When My servant draws close
to Me by the span of a palm, I draw close to him by the space of a cubit, and when he
draws close to Me by the space of a cubit, I draw close to him by the space (covered) by
two hands, and when he draws close to Me by the space (covered) by two hands, I go in
hurry towards him
Allah's Apostle (peace_be_upon_him) said: The finest act of goodness is the kind treatment of a person to the loved ones of his father after his death.
Allah's Apostle (peace_be_upon_him) said: The one who visits the sick is in fact like one who is in the fruit garden of Paradise so long as he does not return.
Allah's Apostle (peace_be_upon_him) said: Be on your guard against committing oppression, for oppression is a darkness on the Day of Resurrection, and be on your guard against petty-mindedness for petty-mindedness destroyed those who were before you, as it incited them to shed blood and make lawful what was unlawful for them.
Source of the above hadith: Sahih Muslim, Book 31