Hadeeth is the application and explanation of the Holy Quraan by the Prophet Muhammad salla Allaho alaihi wa sallam in his words, his actions and his approvals. His approvals mean that a sahaabi did something and the prophet salla Allaho alaihi wa sallam didn't stop him from the action. So he salla Allaho alaihi wa sallam approved the action. The same is the meaning of sunnah, that is how the prophet salla Allaho alaihi wa sallam followed the Holy Quraan. The two things cannot be separated from each other. The Prophet salla Allaho alaihi wa sallam said that he, after him, left two things among us: Allah's Book and his Sunnah, as long as we follow them we will never be astray. ( Allah knows best his prophet's words ). Keeping in mind this meaning and importance of hadeeth and sunnah, I understand that both of them address all mankind. The kalmah Shahaadah is from a hadeeth and all mankind are addressed to it. Of course, the Quraan and hadeeth are both vast sources of knowledge. Some of the verses and ahaadeeth are only for Muslims.