Yes.  The sunnah (what the Prophet Muhammad  said, did, or approved of) is the second source in Islam.  The sunnah is comprised of hadeeths, which are reliably transmitted reports by the Prophet Muhammad’s  companions of what he said, did, or approved of.  Belief in the sunnah is a basic Islamic belief.
	We have, Without doubt, sent down the message: and we will assuredly guard it (from corruption). (Qur'an 15:9) The promise made by Allah (SWT) in Qur'an 15:9 is obviously fulfilled in the undisputed purity of the Qur'anic text throughout the fourteen centuries since its revelation. However, what is often forgotten by many Muslims is that the divine promise also includes, by necessity, the Sunnah of the Prophet (PBUH), because the Sunnah is the practical example of the implementation of the Qur'anic guidance, the wisdom taught to the Prophet (PBUH) along with the scripture, and neither the Qur'an nor the Sunnah can be understood correctly without the other. Allah (SWT) preserved the Sunnah by enabling the companions and those after them to memorize, write down and pass on the statements of the Prophet (PBUH), and the descriptions of his way, as well as to continue the blessings of practicing the Sunnah. Later, as the purity of the knowledge of the Sunnah became threatened, Allah (SWT) caused the Muslim Ummah to produce individuals with exceptional memory skills and analytical expertise, who travelled tirelessly to collect thousands of narrations and distinguish the true words of prophetic wisdom from those corrupted by weak memories, from forgeries by unscrupulous liars, and from the statements of the large number of Ulama (scholars), the companions and those who followed their way. All of this was achieved through precise attention to the words narrated, and detailed familiarity with the biographies of the thousands of reporters of hadith.